Catback: $500+ for approx. 18hp/22 tq.
Muffler & Install: $150 for approx. 8hp/14tq (which is more tq than some catbacks.)
Either way it is a good choice.
I decided it wasn't worth the extra $$$ at the moment and went for the muffler only (with an nice rolled tip) on my '07. I installed a Magnaflow 22", Amsoil filter w/box mod, 2* Timing, and TBS all for $150-200 less than catback with better overall increases throughout.
Sounds really good, not too loud, but deeper and real throaty. Slight drone but nothing that can't be ignored.
As the saying goes:
Speed cost money - how fast do you want to go?
I also went with just the muffler replacement. It sounds good as long as you stay out of the higher RPM's. It makes an unpleasant spattering noise when you do so. But it will do if you are just looking for a throaty sound. A catback system is definitely the way to go.IMO