I pick up a ton of $1000-$1600 cars, many in the 2nd and 3rd bid $2680-$2800 range. With wheels and Aero adds and somewhat decent paint they fetch 40K to 100K on buyout depending on what they are. Any car that's over 100 grand in the dealer that you can pick up for less than 20K can be set at 75K-90K with paint and wheels and sell on buyout 99% of the time.
Some of the common million dollar cars can be had for less than 50K, I stop bidding at 60K. Like the guy above, I add a ton of extras, put a basic handling tune in the car with an appropriate max for an index (..A600, S700..) and a buy out a little lower than the average selling price I usually see or 70-80% of new car dealer cost. It takes me some time to paint with the head, but even futzing for 1/2 a day nets me something easily tweaked for future cars.
I've picked up many cars like the St Ms Mercedes for 20-30K, spiff it nice and get a nice 300K-500K, or more on a good day. Pick up a GTR Spec V for 20K-30K that's loaded @ R1, paint it nice, max it R2 and get 170K on a buyout without having to do anything besides a nice paint scheme but pay for a wheel change, which is 1/2 price cuz you can sell the ugly set that's on it. Paint schemes don't have to be overly complex. Some of the best sales are simply single colors done well, a car with a good visual appeal.
1/2 the cars I buy are cars no one wants or cars that are painted so badly I have to take pity on them so I can strip the paint off it. In fact, the uglier a car is, the more I pay attention to it. Nobody wants an ugly car...
I especially love picking up cars no wants for 1000 bucks and netting a 40-50 thousand buyout for a max class minimal investment car with decent paint and a somewhat unique number. I only do paints once, each one is a little different. When you start getting into higher end sports cars you can get into 100K to 150K buy outs and sell them 90% of the time. When they don't buy out, they still net 75% of the buy out
Last AH outing I put up 9 cars. 1 fell flat, 3 went for what I had in them and 6 went for their buyouts. Got a nice just shy of a mil for appx 60K invested in cars and parts plus a little paint time tweaking the designs to be one offs. Some days are better than others, but on any given 10 cars I clear 1/2 to 2 million, depending on what type of cars I'm selling.
That said, you can ride around many of the rivals and not come close to winning, like the Viper on Indy Road for 5-10 laps and clear 30K plus and get 20K plus EXP and affinity bonuses. Any "stock only" rival usually pays well, and any "race car" rival pays well. Making the bounty is gravy, you still get paid to drive. Every perfect turn, drift, draft or pass makes you cash and XP. It's all money and it's all good. Just have to do it, and you don't have to go online and make up anything.
The drag rivals are really nice. Even in the 10K bounty bracket I cleared a million the other day. Tenthed the field to death an an A594 Dart. Now it's an S642 Dart, and I''m just starting with round two in the 25K bracket. 1/10th-ing the field will get very lucrative now.
I tune myself, but you can buy drag tunes that will get you into the 25K plus brackets all day long. After awhile you'll know who has the best ones. Paying 50K may seem like a lot, but you make it back quick if you want to.
Run a stock car first to get a time, then just race to stay just ahead of your rival, to just beat him once the tune is in. Use the Y button to change your rival, use the X button to find the "nearest me", find a time that's a 1/10th quicker and go. Even if you just reach the 10 K bracket, you can make your 50K back in 10 minutes, double it in another 10. If you're quick on the buttons, you can do it in less time than that.
Not saying this to be special or anything, but I'm far below your average Joe, and I currently have 62 mill after splurging on 30 AH cars the other day. Got 1/2 of them done and ready to go back in. I don't get to drive a ton, most of it is just playing with paint.
The simple truth is the fact I do something. Whatever I can on any given day. Even if it's just taking a stock Devon out for a drive in a Rival just to get the level 5 affinity level. Of course I try to do well, but when up against a tuned super car time, chances are mighty slim. But, the experience in the car, learning a new line in a corner, and the simple fact it pays me. I get $$, I get affinity pay and I get XP. I also now have free Devon parts for the 3 of them I picked up for less than 3 grand apiece in the AH.
Honestly, even with a little effort you can't help but make money in this game. Just drive a rival, any rival. If it pays decent, just run laps. Pays you very well to get better to where you can start riding in the gravy boat. You can even never actually "win" a bounty and make decent cash and XP. Especially for any one that is stock only and gives a shiny new race car to tear up.
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I've actually seen a few cars go for 200M+, and many more for 100M+. The one I spent 84 odd Million on was a Porsche 911 GT2 RS. And yes, that's 350 times its dealership price. I just had to have it. 
