The stock pipes are stainless steel and last a long time. This is the break down of my muffler install:

Ravin Muffler: $100
Installation: $50
Tip: $40
Tip installation: $10

I got it at midas and they recommended keeping my own pipes since theirs were aluminized steel... crappier than stainless. If you don't keep your stock pipes, get mandrel bent pipes.