well, I don't think that you are going to be able to get much for less than $100. Maybe a used o/r h or x off ebay or something. Your best bet is probably just to bank that and save for something a little more, like gears or a catback w/ x or h pipe, open your intake up a little w/ a k&n if you haven't already done so and do the silencer delete (FREE). K&N is going to be under a $100 but probably wont get you much, you could probably find a used CAI off ebay or something. $ for $ though, gears are probably going to be your best mod, but you will have to save.