Before you do anything, you should get gauges. Analog or digital - either will do.
Pyro is required, Transtemp helps if you tow w/ an automatic, and boost is more fun to look at, but is helpful as a trouble shooter.
After that, get an intake - if you're on a budget follow my DIY intake in the wiki files.
After that straight pipe your exhaust to stay on budget - that will give you about 70% of the benefit of a full 4" TB setup (and will cost between 0 and 60 bucks depending if you do the work and how you get thep pipe.)
Then you can try chips - superchips/bullydog/hypertech if you don't want to go too extreme or break the bank. Alll of the above can be had used on Ebay for about 100 bucks.
If you follow this route, you can spend as little as 300 on gauges, 25 on the intake, 0 on the exhaust and 100 on the chip. Basically 500 bucks will buy you almost 100 hp - that's quite a bit for the money. You'll get better fuel mileage if you stay out of it, you will be able to smoke, and depending upon if you have an AUTO or Manual - you can start smokin ricers!