K&N Cold Air Intake, aftermarket exhaust (like Borla, SLP Loudmouth, or Flowmaster depending on what sound you want) Radials, and new gear ratios are all common mods people do and aren't too expensive.

If you're looking for a major acceleration increase without spending much get some 4.10 gear ratios. Probably the best 'bang for your buck' modification... it doesn't increase horsepower but it gives you some really giddy up from the line