take out your resonator (free) and you can drop a k&n filter in if you have about $50.
DIY clear/smoked/colored housing headlights (free. provide your own silicone and blowdryer)
take off your front license plate (free until you get pulled over for it...or in my recent case, until you get a parking ticket and then they give you a ticket for no front plate either)
DIY mesh grill ($5 from home depot)
DIY LED dash conversion ($1.40 to $6 per LED depending if you know where to buy them at. provide your own solder iron, resistors, and skills)
the ever so popular air freshener or broadway convex mirror.
DIY sidemarkers...buy your own.
foglamps ($30 to $600+ depending what kind you want)
tint...not recommended for DIY unless you're good at it.