All you need to do is read all the post in this area and get a very good understanding of the mods available and their cost. But here is a quick rundown.
Rear end gears = Make you quicker also the biggest bang for the buck without going into the motor
Bolt-ons = UDPs, CAI, shift kit and SCT chip programmed for 92-93 octane will give you a nice small increase in power
= Best bang to get big HP period for $600 you get 75-100 HP and slap most of those goofy import guy around like a old rag
Engine Mods = Not the cheap way around but this is singularly the safest way to major HP and a good step to Supercharging