Well, if $600 is too much... either shop for a used cat-back system (I've seen some go as low as $400), or get that flowmaster muffler for $150.

 

There is no question the Z exhaust systems are somewhat over-priced, much of the excess marketing-driven. But, designing a system that will sell well (one that actually adds performance, while being acceptably loud) is not nearly as easy on an engine that is making 80hp/litre, as on one that makes 60 (e.g., Mustang GT). We already have seen exhaust systems for the Z that make no hp difference or even subtract power!

I never thought the day would come when I would spend a $1000 on a catback system, but here it is.