I have had one for 10 years. I cut mostly ranch signs and entryway stuff. Will do some custom work for autos and shops from time to time. Its a sideline, so I rarely turn much down. I charged based on the dimension of the piece (total length x total width x thickness of material) plus design.
These rigs will spoil you. Also, I typically don't cut bolt holes out with the machine. Not only will it harden the edges, plasma will naturally have some deflection, so a drill is necessary to true it up. I typically will pierce a hole for the center, just so it transfers from the CAD file to the piece. Then a visit to the drill press.