I'd definetly get a h22 or h23 engine in there... but i'm sure thats over your budget. Don't be too worried about making your car faster. I assume you're fairly young, right? Not saying this is a bad thing, but because fast cars usually lead to beating on the engine or ending up wrapped around a telephone pole.
With over 200k, I'd say baby the engine. Get as much life out of it as possible. Save up for the engine swap. For the amount of money you would put into modifications, you could spend the same amount on a h22 if you save up.
Also, welcome to the boards!

Take a look around, especially the FAQ sections.