cheap...
remove the air intake silencer, and spring for a k&n air filter. Nice thing about the k&n besides a bit of a power gain is you reuse it, just clean and oil it every 50k miles. Also, when I did my intake silencer and k&n years ago, I remember it sounding cooler than stock in my opinion. I'd rocommend a flowmaster exhaust and custom mandrel bent down-tubes too, but I was too cheap for that myself ha!