250hp from what sort of baseline? Given that a set of dyno's can be anywhere in the neighborhood of 30hp different from one another, it's worth mentioning.
That said, you can spend a lot less on a good turbo. A GT28RS with the .64 A/R turbine housing would work very well, and leave a lot of room to grow into the 300+ hp range if you desire.... and they can be had for a 1K brand new. If you were keeping the output well below 30 lb/min of air you could you something in the GT25 range (SR20DET turbos) for an excellent quick-spooling streetbike (at the expense of peak HP #'s).... it all depends on what you plan to do with said machine. The Comp turbo's are kinda neat, but you have no idea what the compressor efficiency looks like, and an oil-less housing isn't worth 700 bucks in my book. Garrett is the standard IMHO, and I've never been disappointed with one of their turbo's when it was matched to the application correctly.
If you inject water and/or intercool the thing, you can safely run 7-8ish psi (50% increase in baseline hp) all day on a good pump gas tune. The motor internals should be fine at or below that.... though your clutch might not be as forgiving. If you aren't going to run any sort of intercooling you might want to be reeeal conservative on any tuneups over 5psi.... easy to melt stuff after that point on a stock motor.
Advice: Spend good money on your fuel system, engine management, and tune-up.... far more important than which brand of turbo you pick.