the engines are pretty much the same shit for all years (the GSR had the B18C1 in all years)
94-95 are OBD-1 and easier to tune
96+ are OBD-2 they are still tunable but can be a bit trickier... the easiest way is to get a conversion harness and run them OBD-1 then swap back to OBD-2 for emissions testing
the 98+ have better looking lights (IMHO)
as for how much you should expect to spend, that all depends on your area and the condition of the car... check some sites such as autotrader.com, cars.com, and craigslist.com, as well as any local classifieds that you might have in your area