There are tons of posts about mods to do for cheap. Use the search function up top to get some more info or idea's. A Chip should be saved for last so you don't have to have it reprogrammed after you've done more performance mods to your car. For $500 you could buy a MAF adapter, K%N filter, and a Trubendz Catback Exhaust. That will exhaust your funds and will get you to the next step.
MAF adapter -
www.spmotorsports.com - $39
K&N (RU-3530) -
www.ajusa.com - $33
Trubendz Cat-Back -
www.trubendz.com - $340 and up
