I just use the normal cars, I love it when you find a battered up Race-version of a car.
Because you have multiple engine options: I4, V6 and V10.
So you start of with a normal I4, and when you feel like spending money when your car is complete, you swap it for a V10!
After that, Find yourself an American car, or a pick-up. Fix it, sell your old car, and put a BIG V12 in it.
I had the luck to find a pink slip race when I needed cash for a V10, problem solved =D