plasma vs mill/router cnc

We have a farm shop that is pretty well equipped with plasma cutter, several welders, a Bridgeport mill, a couple lathes - none of which are cnc'd. I've been thinking about building a CNC router, or buying/retrofitting a mill, for a long time. But actually think a CNC plasma might be most useful to us. However, I am cheap. I'm thinking a plasma cnc gantry would be pretty easy (cheap) to build - don't need perfect ways, a small amount of backlash is probably livable, the torque requirements shouldn't be significant, and I already have a decent plasma cutter (although I read that e high frequency start might be an issue). What am I missing? Shouldn't this be easy?? thanks in advance, Chuck