I'm in the same boat. Check out the thread titled "Getting ready to Upgrade" for almost all the advice you need.
For a quick answer to your question
steeda.com has an underdrive pulley/balancer that adds 8-10 horses and between it and the belt, you're only looking at dropping about $225.
Also, on some of the 2000's, Ford tappers the exhaust pipe down before it enters the muffler, consider replacing the stock muffler with something like a 2 chamber flowmaster and when you do, keep the pipe constant all the way through.
Lastly, C&L sells a cold air kit for about $250 that boasts 8-15 horses. Check out
C&L's website here.