Cheapest route for a tune is to find someone that has a Tactrix cable and EcuFlash, I can send you a stage 2 tune for your 03 via e-mail. Just flash the tune onto the car with the tactrix and you should be good. Ask on your local forums about it. Another engine management route is the Cobb AccessPort. Personally, I have very little experience with them but I've heard great things about them from the local guys/gals. That's the more expensive route. An AP will run around $400 used and then the tune will run another $100+ unless you use the OTS maps from Cobb which are extremely "safe" tunes.
As for the CEL, if it felt like the car just fell on its face HARD and then the CEL kicked on... It's not the same one.
VF34'd Corvette Killer aka Doug