Lots of choices for exhausts. Greddy, Apexi, HKS, etc.... They are all good. If you want big power for cheap, there is only 1 option. Nitrous oxide. 500 will get you a complete kit. Might I suggest the Zex dry kit. No more then a 55 shot.
http://www.zex.com/
http://www.zex.com/