Well, here is a list of cars which no money can buy.
Pretty big. Especially the part "Prize Crate/Forzathon/Future Specialty Dealer/Milestone Reward Cars"
Thanks to willbsn13 from reddit
Finishing Driver Cup Division Reward Cars
1997 BMW M3 [E36] Forza Edition - Evolution Division Prize
2015 Chevrolet Corvette [C7] Z06 Forza Edition - Forza Drivers Cup Division Prize
2008 Dodge Viper SRT10 ACR Forza Edition - Masters Division Prize
1968 Dodge Dart HEMI Super Stock Forza Edition - Breakout Division Prize
2000 Nissan Silvia Spec-R [S15] Forza Edition - Domination Division Prize
2013 Subaru BRZ Forza Edition - Seeker Division Prize
Showcase Career Reward Cars
1934 Alfa Romeo P3 - Domination Division Showcase
2016 Aston Martin Vulcan - Seeker Division ELITE Showcase
2014 Audi #45 Flying Lizard Motorsports R8 LMS Ultra - Seeker Division Showcase
1989 Audi #4 Audi 90 quattro IMSA GTO - Forza Driver Cup Division Showcase
1967 Brabham BT24 - Breakout Division Showcase
2013 Cadillac XTS Limousine - Seeker Division Showcase
2014 Chevrolet #3 Corvette Racing Corvette C7.R - Breakout Division Showcase
2014 Ferrari FXX K - Domination Division ELITE Showcase
1989 Ferrari F40 Competizione - Forza Driver Cup Division ELITE Showcase
2017 Ford F-150 Raptor - Breakout Division ELITE Showcase
2016 Ford Gymkhana 9 Focus RS RX - Seeker Division Showcase
2016 Ford #66 Ford Racing GT Le Mans - Evolution Division ELITE Showcase
2014 Ford Fiesta ST - - Domination Division Showcase
2010 Ford Crown Victoria Police Interceptor - Evolution Division Showcase
2005 Ford GT - Breakout Division ELITE Showcase
2000 Ford SVT Cobra R - Masters Division Showcase
1985 Ford RS200 Evolution
1975 Ford Bronco - Evolution Division Showcase
2014 Honda #2 Castrol Honda Civic WTCC - Seeker Division ELITE Showcase
2013 Lamborghini Veneno - Masters Division ELITE Showcase
2014 Mazda #70 SpeedSource Lola B12/80 - Evolution Division ELITE Showcase
1998 Mercedes-Benz AMG CLK GTR - Masters Division Showcase
2015 Nissan #23 GT-R LM NISMO - Masters Division Showcase
2015 Porsche #19 Porsche Team 919 Hybrid - Domination Division ELITE Showcase
2014 Porsche 918 Spyder - Breakout Division Showcase
1998 Porsche 911 GT1 Strassenversion - Evolution Division Showcase
1970 Volkswagen #1107 Desert Dingo Racing Stock Bug - Forza Drivers Cup Showcase
Specialty Dealer Cars
1971 Ford Falcon XY GTHO Phase III
2010 Mazda Super20
1995 Nissan NISMO GT-R LM
Prize Crate/Forzathon/Future Specialty Dealer/Milestone Reward Cars
2013 Abarth Punto Supersport
2017 Acura NSX Forza Edition
1990 Alfa Romeo SZ Sprint Zagato
2012 Aston Martin V12 Zagato
2010 Aston Martin One-77
1958 Aston Martin DBR1
2015 Audi S1
2015 Audi S3 Sedan
2014 Audi #67 Rotek Racing S3 Saloon
2013 Audi R8 Coupe V10 plus 5.2 FSI quattro
2010 Audi TT RS Coupe
2001 Audi RS 4 Avant
2013 Bentley Continental GT Speed
2014 BMW M4 Coupe [F82]
2011 BMW 1 Series M Coupe
2011 BMW X5 M
2000 BMW Z8
1995 BMW M5 (E34) - Obtainable through Milestone Rewards
1986 BMW M635CSi
2011 Bugatti Veyron Super Sport - Obtainable through Milestone Rewards
2016 Cadillac ATS-V Forza Edition
2011 Cadillac CTS-V Coupe
2016 Chevrolet Camaro [Gen 6] Super Sport
2014 Chevrolet Super Sport
2014 Chevrolet Super Sport Forza Edition
2010 Chevrolet #99 Green Earth Team Gunnar Oreca FLM09 - Obtainable through Milestone Rewards
1988 Chevrolet Monte Carlo Super Sport
1988 Chevrolet Monte Carlo Super Sport Forza Edition - Obtainable through Milestone Rewards
1971 Chevrolet Vega GT
1970 Chevrolet El Camino Super Sport 454
1970 Chevrolet Chevelle Super Sport 454 Forza Edition
1964 Chevrolet Impala Super Sport 409
1964 Chevrolet Impala Super Sport 409 Forza Edition
1972 Chrysler VH Valiant Charger R/T E49
2013 Dodge Dart [PF]
2013 Dodge Dart [PF] Forza Edition
2012 Dodge Challenger SRT8 392
2012 Dodge Charger SRT8
1969 Dodge Charger Daytona HEMI
2012 Ferrari F12berlinetta
2010 Ferrari 599 GTO
2009 Ferrari 458 Italia
2008 Ferrari California
2004 Ferrari 612 Scaglietti
1963 Ferrari 250LM
2017 Ford GT Forza Edition
2017 Ford Focus RS Forza Edition
2017 Ford F-150 Raptor Forza Edition
2016 Ford Shelby GT350R
2016 Ford Shelby GT350R Forza Edition
2015 Ford Falcon GT F 351
2014 Ford FPV Limited Edition Pursuit Ute Forza Edition
2013 Ford F-150 SVT Raptor Shelby
2009 Ford Focus RS
1993 Ford SVT Cobra R Forza Edition - Obtainable through Milestone Rewards
1977 Ford Escort RS1800
1969 Ford Mustang Boss 302 Forza Edition
1932 Ford De Luxe Five-Window Coupe
2017 Formula E #11 ABT Schaeffler Audi Sport FE02
1988 Holden VL Commodore Group A SV
1977 Holden Torana A9X Forza Edition
2016 Honda Civic Type R Forza Edition
2004 Honda Civic Type-R
1984 Honda Civic CRX Mugen
2014 Infiniti Q50 Eau Rouge
2016 Jaguar F-TYPE Project 7 Forza Edition
2015 Jaguar XKR-S GT
1993 Jaguar XJ220 Forza Edition
1954 Jaguar XK120 SE
2012 Jeep Wrangler Rubicon
2009 Jeep Grand Cherokee SRT8
2016 Koenigsegg Regera
2012 Lamborghini Aventador LP700-4
2010 Lamborghini Murcielago LP670-4 SV - Obtainable through Milestone Rewards
2008 Lamborghini Reventon
1986 Lancia Delta S4
1974 Lancia Stratos HF Stradale
2012 Land Rover Range Rover Supercharged
2000 Lotus 340R
1956 Lotus Eleven - Obtainable through Milestone Rewards
2010 Maserati Gran Turismo S Forza Edition
2016 Mazda MX-5 Forza Edition
2013 Mazda MX-5
2015 McLaren 570S Coupe
2015 Mercedes-AMG GT S
2016 Mercedes-AMG C 63 S Coupe Forza Edition
2013 Mercedes-Benz A 45 AMG Forza Edition
2012 Mercedes-Benz C 63 AMG Coupe Black Series
2012 Mercedes-Benz C 63 AMG Coupe Black Series Forza Edition
2009 Mercedes-Benz SL 65 AMG Black Series
2009 Mercedes-Benz ML 63 AMG
1972 Mercedes-Benz 300 SEL 6.3
2012 MINI John Cooper Works GP Forza Edition
2009 MINI John Cooper Works
1965 MINI Cooper S Forza Edition
2016 Nissan Titan Warrior Concept
2015 Nissan IDx NISMO
1994 Nissan Silvia K's [S14 Zenki]
1987 Nissan Skyline GTS-R (R31)
1973 Nissan Skyline H/T 2000GT-R
2012 Pagani Huayra
2009 Pagani Zonda Cinque Roadster
2000 Plymouth Prowler
1973 Pontiac Firebird Trans Am SD-455
2016 Porsche 911 GT3 RS [991.2]
2015 Porsche Macan Turbo
2012 Porsche 911 GT3 RS 4.0 [997]
2011 Porsche #45 Flying Lizard 911 GT3-RSR
1957 Porsche 356A Speedster
2013 Renault Clio RS 200
2016 Rolls-Royce Dawn
2005 Subaru Impreza WRX STI
2005 Subaru Legacy B4 2.0 GT
1998 Subaru Impreza 22B STi Forza Edition
1980 Subaru BRAT GL Forza Edition
2017 TAMO Racemo
2005 TVR Sagaris
2011 Volkswagen Scirocco R
1995 Volkswagen Corrado VR6
1981 Volkswagen Scirocco S
1963 Volkswagen Type 2 De Luxe
2016 W Motors Lykan HyperSport
Pretty big. Especially the part "Prize Crate/Forzathon/Future Specialty Dealer/Milestone Reward Cars"
Thanks to willbsn13 from reddit
Finishing Driver Cup Division Reward Cars
1997 BMW M3 [E36] Forza Edition - Evolution Division Prize
2015 Chevrolet Corvette [C7] Z06 Forza Edition - Forza Drivers Cup Division Prize
2008 Dodge Viper SRT10 ACR Forza Edition - Masters Division Prize
1968 Dodge Dart HEMI Super Stock Forza Edition - Breakout Division Prize
2000 Nissan Silvia Spec-R [S15] Forza Edition - Domination Division Prize
2013 Subaru BRZ Forza Edition - Seeker Division Prize
Showcase Career Reward Cars
1934 Alfa Romeo P3 - Domination Division Showcase
2016 Aston Martin Vulcan - Seeker Division ELITE Showcase
2014 Audi #45 Flying Lizard Motorsports R8 LMS Ultra - Seeker Division Showcase
1989 Audi #4 Audi 90 quattro IMSA GTO - Forza Driver Cup Division Showcase
1967 Brabham BT24 - Breakout Division Showcase
2013 Cadillac XTS Limousine - Seeker Division Showcase
2014 Chevrolet #3 Corvette Racing Corvette C7.R - Breakout Division Showcase
2014 Ferrari FXX K - Domination Division ELITE Showcase
1989 Ferrari F40 Competizione - Forza Driver Cup Division ELITE Showcase
2017 Ford F-150 Raptor - Breakout Division ELITE Showcase
2016 Ford Gymkhana 9 Focus RS RX - Seeker Division Showcase
2016 Ford #66 Ford Racing GT Le Mans - Evolution Division ELITE Showcase
2014 Ford Fiesta ST - - Domination Division Showcase
2010 Ford Crown Victoria Police Interceptor - Evolution Division Showcase
2005 Ford GT - Breakout Division ELITE Showcase
2000 Ford SVT Cobra R - Masters Division Showcase
1985 Ford RS200 Evolution
1975 Ford Bronco - Evolution Division Showcase
2014 Honda #2 Castrol Honda Civic WTCC - Seeker Division ELITE Showcase
2013 Lamborghini Veneno - Masters Division ELITE Showcase
2014 Mazda #70 SpeedSource Lola B12/80 - Evolution Division ELITE Showcase
1998 Mercedes-Benz AMG CLK GTR - Masters Division Showcase
2015 Nissan #23 GT-R LM NISMO - Masters Division Showcase
2015 Porsche #19 Porsche Team 919 Hybrid - Domination Division ELITE Showcase
2014 Porsche 918 Spyder - Breakout Division Showcase
1998 Porsche 911 GT1 Strassenversion - Evolution Division Showcase
1970 Volkswagen #1107 Desert Dingo Racing Stock Bug - Forza Drivers Cup Showcase
Specialty Dealer Cars
1971 Ford Falcon XY GTHO Phase III
2010 Mazda Super20
1995 Nissan NISMO GT-R LM
Prize Crate/Forzathon/Future Specialty Dealer/Milestone Reward Cars
2013 Abarth Punto Supersport
2017 Acura NSX Forza Edition
1990 Alfa Romeo SZ Sprint Zagato
2012 Aston Martin V12 Zagato
2010 Aston Martin One-77
1958 Aston Martin DBR1
2015 Audi S1
2015 Audi S3 Sedan
2014 Audi #67 Rotek Racing S3 Saloon
2013 Audi R8 Coupe V10 plus 5.2 FSI quattro
2010 Audi TT RS Coupe
2001 Audi RS 4 Avant
2013 Bentley Continental GT Speed
2014 BMW M4 Coupe [F82]
2011 BMW 1 Series M Coupe
2011 BMW X5 M
2000 BMW Z8
1995 BMW M5 (E34) - Obtainable through Milestone Rewards
1986 BMW M635CSi
2011 Bugatti Veyron Super Sport - Obtainable through Milestone Rewards
2016 Cadillac ATS-V Forza Edition
2011 Cadillac CTS-V Coupe
2016 Chevrolet Camaro [Gen 6] Super Sport
2014 Chevrolet Super Sport
2014 Chevrolet Super Sport Forza Edition
2010 Chevrolet #99 Green Earth Team Gunnar Oreca FLM09 - Obtainable through Milestone Rewards
1988 Chevrolet Monte Carlo Super Sport
1988 Chevrolet Monte Carlo Super Sport Forza Edition - Obtainable through Milestone Rewards
1971 Chevrolet Vega GT
1970 Chevrolet El Camino Super Sport 454
1970 Chevrolet Chevelle Super Sport 454 Forza Edition
1964 Chevrolet Impala Super Sport 409
1964 Chevrolet Impala Super Sport 409 Forza Edition
1972 Chrysler VH Valiant Charger R/T E49
2013 Dodge Dart [PF]
2013 Dodge Dart [PF] Forza Edition
2012 Dodge Challenger SRT8 392
2012 Dodge Charger SRT8
1969 Dodge Charger Daytona HEMI
2012 Ferrari F12berlinetta
2010 Ferrari 599 GTO
2009 Ferrari 458 Italia
2008 Ferrari California
2004 Ferrari 612 Scaglietti
1963 Ferrari 250LM
2017 Ford GT Forza Edition
2017 Ford Focus RS Forza Edition
2017 Ford F-150 Raptor Forza Edition
2016 Ford Shelby GT350R
2016 Ford Shelby GT350R Forza Edition
2015 Ford Falcon GT F 351
2014 Ford FPV Limited Edition Pursuit Ute Forza Edition
2013 Ford F-150 SVT Raptor Shelby
2009 Ford Focus RS
1993 Ford SVT Cobra R Forza Edition - Obtainable through Milestone Rewards
1977 Ford Escort RS1800
1969 Ford Mustang Boss 302 Forza Edition
1932 Ford De Luxe Five-Window Coupe
2017 Formula E #11 ABT Schaeffler Audi Sport FE02
1988 Holden VL Commodore Group A SV
1977 Holden Torana A9X Forza Edition
2016 Honda Civic Type R Forza Edition
2004 Honda Civic Type-R
1984 Honda Civic CRX Mugen
2014 Infiniti Q50 Eau Rouge
2016 Jaguar F-TYPE Project 7 Forza Edition
2015 Jaguar XKR-S GT
1993 Jaguar XJ220 Forza Edition
1954 Jaguar XK120 SE
2012 Jeep Wrangler Rubicon
2009 Jeep Grand Cherokee SRT8
2016 Koenigsegg Regera
2012 Lamborghini Aventador LP700-4
2010 Lamborghini Murcielago LP670-4 SV - Obtainable through Milestone Rewards
2008 Lamborghini Reventon
1986 Lancia Delta S4
1974 Lancia Stratos HF Stradale
2012 Land Rover Range Rover Supercharged
2000 Lotus 340R
1956 Lotus Eleven - Obtainable through Milestone Rewards
2010 Maserati Gran Turismo S Forza Edition
2016 Mazda MX-5 Forza Edition
2013 Mazda MX-5
2015 McLaren 570S Coupe
2015 Mercedes-AMG GT S
2016 Mercedes-AMG C 63 S Coupe Forza Edition
2013 Mercedes-Benz A 45 AMG Forza Edition
2012 Mercedes-Benz C 63 AMG Coupe Black Series
2012 Mercedes-Benz C 63 AMG Coupe Black Series Forza Edition
2009 Mercedes-Benz SL 65 AMG Black Series
2009 Mercedes-Benz ML 63 AMG
1972 Mercedes-Benz 300 SEL 6.3
2012 MINI John Cooper Works GP Forza Edition
2009 MINI John Cooper Works
1965 MINI Cooper S Forza Edition
2016 Nissan Titan Warrior Concept
2015 Nissan IDx NISMO
1994 Nissan Silvia K's [S14 Zenki]
1987 Nissan Skyline GTS-R (R31)
1973 Nissan Skyline H/T 2000GT-R
2012 Pagani Huayra
2009 Pagani Zonda Cinque Roadster
2000 Plymouth Prowler
1973 Pontiac Firebird Trans Am SD-455
2016 Porsche 911 GT3 RS [991.2]
2015 Porsche Macan Turbo
2012 Porsche 911 GT3 RS 4.0 [997]
2011 Porsche #45 Flying Lizard 911 GT3-RSR
1957 Porsche 356A Speedster
2013 Renault Clio RS 200
2016 Rolls-Royce Dawn
2005 Subaru Impreza WRX STI
2005 Subaru Legacy B4 2.0 GT
1998 Subaru Impreza 22B STi Forza Edition
1980 Subaru BRAT GL Forza Edition
2017 TAMO Racemo
2005 TVR Sagaris
2011 Volkswagen Scirocco R
1995 Volkswagen Corrado VR6
1981 Volkswagen Scirocco S
1963 Volkswagen Type 2 De Luxe
2016 W Motors Lykan HyperSport