Sounds like you've just described a CNC machine. I have one like this:
... and it was less than ?200 at Christmas. If you are wedded to the paint idea (to later etch), then you replace the bit with a needle and experiment whether rotating the needle has benefits. If that doesn't work out then you can put the cutting bit back and mill the tracks as DuWayne shows in the above link.
73
Tony G4WIF
