I bought an exhaust pipe cutter at Harbor Freight last year. It'a kind like big pair of pliers that clamp around the exhaust pipe. There are 4 cutting wheels, evenly spaced, like on a pipe cutter. Hardly need any clearance to use. it... just move the handle back and forth a few times (1/4 turn or so) and you have a clean, square cut. I used it on steel pipe, seems it should be good for stainless, too. I got the $20 cheapie, they had a heavy duty version for $10 - $20 more.
It would be just the thing to use if you're financing your hobby by stealing Cat Converters!