I use the diamond cut-off wheels, because I always break the normal cheap ones before I even begin to cut anything. I don't know if my cheap ones are extra-cheap or if it's just my usual unsteady hands (I'm terrible at doing things freehand).
Either way, I can get replacements cheap at Harbor Freight.
10 pc rotary rasp set, $5.29: http://www.harborfreight.com/cpi/cta...emnumber=35453
5 pc rotary rasp set, $4: http://www.harborfreight.com/cpi/cta...temnumber=4476
5 pc diamond cut-off wheel set, $3: http://www.harborfreight.com/cpi/cta...emnumber=31501
Even at that price I can't currently afford to waste them, so I'll have to be careful to go slow. I have cut plastic before and it definitely does melt, though it never seems to stick to the cutoff wheel.
Edit: I got an idea...abrasive blade on circular saw, with the circular saw mounted as a tablesaw. That ought to cut the stuff easy and those blades are incredibly cheap. Hospital, here I come!