For a Plug-n-go electronics solution WITH Digital Torch Height Control see our
http://www.candcnc.com/PlasmaPakPriceChart.htm It's everything you need between the PC and the mechanical part of the table. You can pick from stepper (suggested for tables of your size) or servo based systems.
You should be able to build a complete plasma table with full electronics including the DTHC for about 1/2 or less of a commercial rig.
my advice needs to be taken in the context that I have something to sell so just add it as part of your research. (:-)