What Bill said, with the exception that I'd recommend staying far, FAR away from "build up gradually."

If you are in a position where you can only afford to put a small amount of $$ into the car at a time, open a savings account and put the money there instead. THEN, when you've got the $$ together, buy an already-built car. I guarantee you will be on the track sooner, and if something happens that derails your plan, you'll still have the dough rather than a garage full of parts worth pennies to the dollars that you spent buying them.

I've got about $400 worth of parts on my race car that I bought from people liquidating parts - meaning that I spent a lot less than half that value to take the bits off those guys' hands.

K