Lemmie get mah spoon...
90-93: Nothing wrong with them really, other than the weak *** rear end and the fact that 1.6l is less than 1.8l. You WILL be replacing the rear carrier/diff/axles/driveshaft/brakes/clutch if you expect to get anywhere near your power goal. Good news is that all these parts are easily sourced from 94-05 cars. Adjustable FPR can eliminate the need for super big injectors depending on power level. MSPNP9093 are pretty cheap used, get one with IAT and remove that funky AFM. Greddy kits are also cheap and plentiful. Lightest Miatas out there. Bad news is the 90-ish cars cranks break or something, search for "short nose crank." VLSD is also suck
94-95: 1.8l is more displacement, better rear carrier/diff/axles/driveshaft/brakes/clutch. Same type of fuel system but with bigger injectors. MSPNP9495 is available for management. Slightly stiffer chassis than the 90-93, but not amazing my any means. Slightly stronger 5spd trans (IIRC?) Stronger Torsen diff also available. Lightest 1.8 cars out there.
96-97: Basically the same as 94-95 except for more chassis bracing. Slightly stiffer, slightly heavier, slightly more power with 9:1 comp ratio bump. Again, MegaSquirt delivers with MSPNP9697. Last of the 1.8 NA cars, so almost all the bugs are worked out.
99-00: The NB1 model. No more pop-up headlights, better brakes, revised BP4W head makes more powah by flowing more oxygens and pistons give bump in compression ratio (9.5:1). Issues include bad thrust bearings in the early 99 engines that cause the (you guessed it) cranks to break. Some of these cars are built as "California Models" and have goofy *** emissions controls and dual cat converters. Faulty coil packs leading to catalytic converter Chernobyl action make them (sometimes) cheap to pick up once the owner sees the $1,000 replacement cat cost. Fuel system is returnless system so adjustable FPR is not usually an option without tons of work. Some of the 99's have a 6 speed trans that is sex. TorsenII diff is also out there and is also sex. There is no true PNP ECU option, but you can always DIYPNP a MS2 or look for one of the guys on the forum that offer to build them as a service.
01-05: NB2 models. Mostly the same as 99-00 except 10:1 comp ratio and new fangled VVT intake cam crazyness. DIYPNP + VVT controller for the ecu for the MS2 flavor. Engine issues sorted out and stiffer chassis, cars get heavier as they get closer to 05. IIRC TorsenII was replaced for the less desirable Tojici-Fujitsi thing in 04-05 models.
04-05 MazdaSpeed Miata: Out of your price range. Comes with turbho from the factory.
06+: More monies
That's all I can remember right now... IMHO buy the newest, best condition, lowest mile, minimally molested car you can find. Be prepared to wait and be choosy. Car with a removable hard top is usually not a bad idea.
If any of this makes no sense, go visit Miata.net and search there garage section and use the googles.
Also, you now owe me beer
PM me for paypal address to send beer monies.