Yea depends on budget and type of motorsport you want to get into.
At the tighter budget end id go for a s13, they are coming up cheaper and cheaper in the trader and parts are a dime a dozen. The other budget option would be a vn commo or ea falc saloon car - prob 10 - 15 k will get you a race ready car, complete roll cage, prob a shit load of spares, reasonably straight foward to super or even turbo charge......
deeper pockets though, a some hae suggested, they skys the limit.....