well, you can get a aem CAI(cold air intake) from ebay for about 180. that is the cheapest you will find a new one though. you can always get one off ebay that just replicaztes and costs 40 bucks, but fitment may not be perfect. either way, i would get an aem bypass valve, to make sure your cai doesnt suck up any water from the road and give your engine hydrolock. a newer catback system will definately help gain you some power. the MBRP cat back is prolly the best one for our cars.
check out the forums at
www.rdtiburon.com.
there is a possible group buy for MBRP catbacks right now in the group buy section. i am the same tibby01 on that forum too. it is specifically for our model tiburon(the "RD" tiburon), and everyone is a great help.