I'd try to find a car that already had most of the parts you need. Race cars often come on the market, some because the driver lost interest, and some because the driver outgrew them.
Either way, you can get the car for pennies on the dollar vs having to buy/build everything from scratch.
As for which is better, I'll predict that you will find more inexpensive ex-racing foxes for sale than the later models - but either way, the decision would depend on just what you were getting for your money.
I'd let the dollars enter into the equation.
I think I just saw a few cars that might fit the bill. I'll see if I can link them to this thread later.
Cars For Sale: Car Details - AutoTrader.com Cars For Sale: Car Details - AutoTrader.com Cars For Sale: Car Details - AutoTrader.com
First car is potential track/street candidate.
2nd car is already for the track, but could easily be modified for track work (suspension and brakes, of course).
Third car is road racer (and cheap at the price).