Z31 is an overlooked bargain, the turbo offers a lot more performance, the n/a can be converted but it's a fairly involved swap and not for the novice, 3k definitely buys a nice one these days.
MR2's the 85-86 was available only as an n/a, horribly slow but great fun to drive, amazing handling car. The 87-89 was available with the supercharger which isn't fast but certainly an improvement. There are ways to add power to both, both are drop dead dependable. shifter is by cable and feels vague, there are brass bushings to improve this but still nothing like a miata (miata has one of the best factory shifters available bar none). Prices on the aw11 MR2's is on the rise, getting harder to find decent cars for $3k but they are still out there. the engine has to come out the bottom which is a pita but once you get used to it it's still easier than working on a z32.
The sw20 MR2 (90-96) was available as a turbo, still dependable, larger engine bay but the engine packaging was horrible and made it even more difficult to service, the engine still drops out the bottom, the turbo has loads of power potential, $3k can buy a drivable turbo car these days. It's a bigger nicer driver than the AW11 and a better daily driver that still handles like a dream.
If you are really retarded you can do the MK1.5 swap, you take the turbo engine (3SGTE) form the SW20 and swap it into the AW11, it's definitely an advanced swap, as the frame horns must be cut out and new ones fabbed and welded in. I did this, I don't recommend it
http://502streetscene.net/forum/showthread.php?t=192988
You didn't mention miata but it's a lot of fun for the money. drop dead dependable, easy to work on, loads of resources both replacement and performance, engine swaps turbo's whatever you want it's out there, and just as practical as an mr2. and 3k gets you a nice na (89-97) maybe even a high miles nb (99-05)