2.5RS L? Is it a swap? Well, it doesn't matter, same car basically. If you feel spendy, I'd say Stromung. Blitz, Scooby Sport, and Apex are pretty popular. Probably the best bang-for-the-buck is the full MRT header back- it'll give you as much power as any combo and will only cost about $800 new. On a budget, I'd say Borla headers and a custom catback, with a Magnaflow or Flowmaster muffler. That shouldn't top $450 total, since you can get Borlas for $270 shipped from iSR performance.

 

Just my 2 cents...I think the GReddy EVO cat-back looks the best, as for performance, the Cobb exhausts always win the power gain tests.