the question you need to start with is how competitive you want to be. A competitive *anything* will be more expensive than you plan on. There are 45,000 dollar Spec Miatas running around. Of course, you could build one that's "legal" for less than 10...

karts are the same way....a nice one is 5, a GOOD one is 10...etc.

for now, id suggest doing as many track days as possible. far less risk, you get instruction, you go as fast as you want to without dealing with real traffic...etc.

Chin, SafeMotorsports, BMWclub, PCA, thats where you should go for now IMO.