I'm not sure if your machine is going to handle the forces of cutting. Remember when you cut with a router, you're causing actual forces on the structure vs a plasma where the torch just floats above everything.
I'd look to grab something like a Bosch Colt for $100 and home brew a mount. I wouldn't spend too much. If it all works out, then you could look into a .8KW or 1.5KW air cooled spindle from China.