I can tell you that the driver is the most important part of the car. The best money spent is on track time and coaching!!!!!! That being said I can also tell you that the car is also important.
I spent well over $30K developing my RX7. I started with a street car and had a no expenses spared race car built professionally. After 3 seasons we have finally worked the bugs and gremlins out!!!!!! Just in time for me to move to an SSC car to run nationals. I can tell you it would be better to BUY a WELL DEVELOPED car in GOOD condition and save yourself some aggrevation and money. To buy a cheaper car with possible issues is not the way to go.
The money that you save by buying a GOOD car should then be spent on track time and coaching from a qualified coach!!!!!!!