Gutted cats are cheap to do (costs only about $15 for each MIL eliminator, substantially less if you take a trip to Radioshack and make your own). Thus, gutted cats will run $30. High flow cats will set you back a couple of hundred bucks.

Personally, I am going to be very pragmatic with any mods that I do to my car. My previous ride had a ton of aftermarket stuff on it, and as a result, it was stiff riding, loud, buzzy, and a lot more difficult to live with. Though not as much as speed, refinement is addictive in its own right. And, refinement is one of the things that the Crossfire does exceptionally well (for a sports car).