well the muffler shop fix option only costs $20 or so, so if youre worried about the price of a new cat, you could do that and just worry about it later. The beauty of building up a car like this is you can do it a little at a time. You could just get the catback and the intake, for instance, and then a few months later, or a year later or whatever, get the header and the cat.

And its not just the HP to worry about.... actual power increases will be minimal, but throttle response will be greatly improved, as will the bling factor. It'll just make the car more of a pleasure to drive in general.