As Poser said, take it to a local shop. If you feel as though you are unsure if they are quoting you the best price/service, get a second and third quote.
I went to my local muffler shop and got a 18" round muffler and had the guy do the bends and I welded it together myself. it was $40.00 total cost with the flange and gasket.
There are pics on here somewhere....when I had to make my muffler decision some were posted.....
I ended up going to Monroe Muffler....I took them a basic muffler and told them how I wanted it routed....They'll do what you want and the prices are more than acceptable....$80.00 for my trip....My muffler, their exhaust pipe and labor/welding....
Search for exhaust fumes to read on where you need to have your exhaust exit......After the rear Drivers side tire for me....
I had a local muffler shop do mine. They ran it through the skid plate and stuck a flowmaster 40 series on there. Sounds good. You can save some money by buying your own muffler. Any turbo muffler should sound better than stock.
Guys, we are running straight 6 motors. They will never sound like a V8. I would be more concerned about back pressure and flow restrictions when purchasing a muffler and exhaust system.
The best sounding 135 I have heard was Mark's (Marksoffroad.net). Although it wasn't as loud or low as a V8, it had a great tone and purred like a (forgive the simile) lion.
On my 73, PO put a cherry bomb on it and a resonating tail pipe. Sounds good to me and gets good flow. I haven't felt the need to change it.
One main concern it where you dump your exhaust. My personal opinion is dump it right behind the rear tire facing the side (either side). If you run it straight out the back, it will get sucked back in even with a hard top (they are not air tight). I found when they dump right next to the driver or passenger door, the fumes still make it in the rig when driving and the floor boards get REALLY hot right there.