I agree, most real commercial plasmas use helical RP. I will not insist further on ball screws,though they could be protected or dust evacuated in a downdraft table like i said. Obviously the less hassle, the better.

I don't know prices, but if he likes as he said "ready elements" he could look at Bell Everman "servo belt". Or try to construct similar belt on belt mechanism. I assume that 2 belts protect each other from dust in between, upside down and hidden.