One of the biggest bangs for the buck would be a cam change. Add an intake, exhaust and you are looking at close to 100 hp w/stock heads easily. Beyond that, and you start looking at parts above $1000. Keep in mind depending on your choices, you may need somebody to look at your programming and may need to make some adjustments. Your best bet is to give competition cams a call, let them know exactly what you have, exactly what you are looking to do and they will let you know what to do.