Cheapest route, get a used vf39/48/52 along with walbri 255, STI pink injectors, sti intercooler, ebcs, tune. Should get you a very noticeable power upgrade, *shouldnt* blow your engine, and be pretty cheap ( easily under 2k).
Better would be 16gxtr, spearco tmic, 750cc injectors, walbro 255, ebcs and a tune. That's going to be significantly more expensive, but also a much better setup more power, more area of improvement when you get bored with the power, and a better powerband. Plus still capable of E85 if you want.