If I were to buy a front pipe, high flow cat, muffler, and tail pipe for my 91 XJ, about how much do ya'll think it would cost to have it professionally done? I called my mechanic, and I got an "It all depends".

or

I have a friend with a welder. Is putting this stuff on hard or easy?

 

If your friend has a welder than that job is a piece of cake. Some of it can probably be clamped or bolted together. Some aluminized band clamps can make for a very clean installation, rather than using the POS muffler shop U-clamps that turn into rust in a short time.