I've done my own exhaust systems 3 or 4 times now. I'll spend about $300 or so in mufflers and pipes/bends, then cut and weld them all together myself, ensuring a great fit, and no leaks.

might not be any cheaper, especially for the guys who say "yea, but your time costs money!!" I look at it as "I get to spend a day relaxing in the garage fabricating and welding"