Swap a WRX or STI in a 2.5rs

Not exactly sure what ur question is.

Is it possible? Yes it is.
Is it a good idea? l think so Yes.
How much does it cost? 7-10 thousand dollars depending on how much u do yourself (maybe less if u can find a very cheap WRX engine)
What do u need? Motor (transmission is a good idea too), a turbo crossmember to allow room for the tubo exhaust, a hood with a intercooler vent, unless u buy a front mounted intercooler, a wiring diagram & a lot of patience.

l am not sure if I've answered ur question because it is not really clear what u want to know, but l hope I've been able to help.

l guess it all depends on what type of car u want. If u r looking to rally l would go with a 2.2l because of the strict guidelines. But if u r looking to smoke all those sticker racer wanna-bees, go with an STI. They r built a bit better to withstand the pressures of an everyday racer, plus the American version is a 2.5l & u know the more displacement the more power u r capable of achieving. l once read an article on someone who set out to build a1000hp scoobi monster. l missed out on the final article & am still trying to find it. l am sure he accomplished his goal. Never the less the WRX & ST l r virtually the same besides a few hopups & more fine tuning, but this all comes at a higher penny.