You could also make your own circle cutter with some shaft collars. Get one collar that will fit your plasma torch. Weld a piece of 3/8" round bar to the collar that fits the plasma torch. Get a 3/8" collar and weld a 1/8" piece of round stock to it so it will be your center point. The 3/8" collar will slide up and down the 3/8" round stock making it adjustable. It would probably cost you $10.00 to make, and you would have an adjustable hole cutter.

Swagg Offroad has one that's not to pricey.