Depends on what your plans are for the car. Are you talking about engine performance? Suspension performance? Braking performance? I will assume you are talking about accelerating faster, which is what most people want to do. Again, depending on what your plans are for the car, you could buy a good cone filter and make your own intake for under $50. Spend a couple hundred more on an aftermarket header, and either an ebay special exhaust, or have something custom fabbed up at the local exhaust shop. You could gain around 10hp to the wheels. Or, if you just want to go fast right now, pick up a nitrous oxide kit and get 50hp to your wheels relatively safely.