There is a gold mine of very reliable plasma cutting systems sitting idle in old warehouses, the back of your or your buddy's shop, on eBay, or at an estate sale. When I started my business, these machines were everywhere. They were straightforward; they basically had two or three very robust transformers, simple rectifiers, a simple repairable PC board, and a simple high-frequency start circuit. They usually had two or three current transformers for cutting. One for lower amps, this transformer adds to the second, giving you a middle range, and all three are paralleled to offer the highest cutting current. All connected with the same style of contactor. All analog power control items that could easily be repaired in the field.