An axle back or cat back won't any difference on this car when you're N/A. Its purely for sound and looks. I'd suggest keeping an eye on the classifieds to see if there's something that you like. For example, I picked up a Q300 and catless front pipe for 400 bucks.
As @
mav1178 said, the only carb legal turbo kit is the works kit since you keep the factory header. However, there are a few carb legal supercharger kits available. Jackson Racing, Kraftwerks and Edelbrock are the ones that come to mind.