Want to unlock Concept Cars? Then in Career mode you have to get the following Kudos:
10,000: Ford Mustang GTR
50,000: Nissan GTR
90,000: Cadillac 16
120,000: Ford Supercar Concept
160,000: Shelby Cobra
230,000: Toyota GT-One
300,000: Ford GT90
390,000: Shelby GR-1
475,000: RUF Supercar Concept