[eion]

Well, I'd get the newest car you can afford. The caveat to this is that a better-maintained older car will be better than a new car that hasn't been maintained. You should be able to get a very decent early ('90 or '91) 964 within your budget. Depending on where you are (you don't say), you may be able to find newer cars, but I would shy away from these, as at this price they're not going to have been as well looked-after. I'm sure you've heard all the horror stories about the early 964s, but as long as all the maintenance has been done and the PPI checks out, they're perfectly good cars.

edit:
just saw your comment on the turbocharger. Any decent aftermarket turbo is going to be spendy ($10k minimum from what I've seen), and may effect how smoggable etc. the car is. You might want to go with a factory turbo instead - this'll have upgraded everything (brakes, drivetrain, etc.) to go with the extra power.