You gonna get flamed for not using the search function... Specially about this series. There are about a million posts on the GTWC.
But since so many people have asked the same question I happen to have a handy piece of text to copy and paste. Make sure you follow all of the links....
Read this first
https://www.gtplanet.net/forum/showthread.php?t=61462
Then, be aware that there is no need to worry about buying a car. You can do it with a number of prize cars and pretty much $0 if only you can get yourslef to wait a little longer.
To get to 25% on almost $0 read
https://www.gtplanet.net/forum/showthread.php?t=64368
To get to 50% on less than 50k read
https://www.gtplanet.net/forum/showthread.php?t=66151
To get to 70% on less than 100K read
https://www.gtplanet.net/forum/showthread.php?t= 67134
Once you have enough prize cars you can choose to do the GTWC with any of the following prize cars
Toyota Minolta 88CV read about it here
https://www.gtplanet.net/forum/showthread.php?t=67885
Bentley speed 8 read about it here
https://www.gtplanet.net/forum/showthread.php?t=67803
AMG CLK-CTR read about it here
https://www.gtplanet.net/forum/showthread.php?t=61647
Jaguar XJR-9 read about it here
https://www.gtplanet.net/forum/showthread.php?t=66530
NISSAN MOTUL PITWORK Z (JGTC) '04 read about it here
https://www.gtplanet.net/forum/showthread.php?t=66134
Zonda LM read about it here
https://www.gtplanet.net/forum/showthread.php?t=64108
Non Prize Cars
Pescaroly C60 read about it here
https://www.gtplanet.net/forum/showthread.php?t=66579