The artofcnc.ca Mach2 software is $150 and it has plasma cutting abilities. It also runs stepers through parallel port. In the mach2 documentation pdf there is even a schematic and detials on a torch-height adjustment feature. many users seem to really like artofcnc software.
for CAM I dont have any idea. id imagine for Plasma cutting, you need to mostly follow DXF lines. no 3d anything.. you can try importing DXF right into mach2. the demo version runs 2000 lines of code, so thats enough to do a bunch of tests.
good luck
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