what is your bench top mill. ? read my x-2 conversion post .
the stirling steel plans are probably the easiest to make parts. if I were converting a mill I would likely go the gecko 540 route with gecko motors. If you can handle ubuntu/linix os then go for emc2 software that is the cheapest. cnc take time and commitment to learn. The Home shop Machinist/ Digital machinist Mags hold a CNC seminar in Michigan last year the had a cnc team build each guy went home with a converted mill. IIRc it was just under $3000 for everything. could be an option if you are patient . I will say doing a conversion on your own is an adventure.
Tin