I have a 91 nx2000 w/ sr20de. Im rebuilding the engine right now and im debating on the turbo. Can i get a t25 or t28 (prefer a t28 ball bearing) for like $500 or less? If so where? A t28 kit for it is a bit above 2k i think. After its all done, would the kit just be cheaper? And would the preformance be worth the money?

You can probably piece it all together from this forum for under $800? T25 vs T28 cost is not going to differ much. BB will cost more.

is the preformance from a t28 worth the money? they're relatively small right?

For the extra cost its worth it if can find a deal. A t25 will get you plenty of hp for a small turbo, my first t25 setup made 258hp at the wheel on only 10psi.