best bang for your buck would be IMO a cold air intake and a tuner if you don't have that yet, then gears, once you have the tuner you will be able to correct your speedomoter when you get gears and also have one of the few custom tuners write and email you a tune for your car, gears might be cheap to buy but labor to install is another story, shifter is a cheap and easy mod that you can do yourself.