um some cost effeciant upgrades would be
1. Intake
2. New computer chip for fuel/air flow
for the intake try here
http://www.weapon-r.com/ : these intakes are quality, a few of my friends have these...i personally like them, although i would suggest just finding a cheaper version...seeing as most of them all do the same...add 5-10hp and add an awesome throaty throttle sound....as cool as an exhaust..just less annoying