After recently purchasing a SW20 myself, I found that the cheap SW20's just arn't worth your time, I looked at a few for around the $11.5K mark, cheapest I could find at the time. They didn't drive particularily well, body was ok, but surely the drivetrain/engine is more important.
I would say based on what I bought anywhere from $13K-15 gets you a average to good SW20 and above that would be a mighty fine one, $18K+ would get you a import GT.
I found some nice ones on carsales.com.au quite alot of MR2's there actually.