Toyota MR2 - Buyers Guide - Sport Compact Car Magazine
Start from there. Pretty thorough and comprehensive guide.
You can get an NA for cheap...if you're looking for a track car, you'll find one in the 1-2K price range with a blown motor, probably ****** condition seats, body damage etc. If you're looking for something MINT, you're probably going to be paying 3-5K. Then, a JDM Gen II (w/ 225whp) turbo rear clip will cost around 2500, a JDM Gen III (w/ 245bhp) turbo rear clip will cost around 3000-3500, 93+ turbo brake swap will cost anywhere from $500 to $1000, and then you have to do all the labor in swapping everything over.
Also, if you get 93+ brakes, you can't run the puny 91 NA wheels because the caliper won't clear, so you'll either have to find one with aftermarket wheels or get some 93+ wheels or your own aftermarket wheels.
I think the headache isn't worth it and it's better to find a car with a well done Gen III swap with good compression and possible a 93 turbo chassis. It might cost in the neighborhood of 10K-11K, but the turn-key sports car factor is a plus.
But all this is in my opinion and should be taken with a grain of salt.