This would be for PCBs, and will be a bootstrapped effort.
Build volume of 4″x4″
Three cutter heights with a travel of 3/8″ being plenty
Use a generic (Harbor Freight) rotary tool
Either drive everything directly off an Arduino or through-hole some stepper motor drivers
Have a build plain with mount holes to keep everything in alignment and flat
Build a jig for drilling these mount holes
Have the mount holes be offset slightly so the PCB will be keyed in case I ever need to do a double sided board