I would be looking at a Ajax CNC kit, it's a true DC servo system, a great bang for the dollar. You should be able to use the DC servo motors that are on the mill right now.
Try to stay away from these low cost hobby controllers, with steppers, or step driven wana be servo drivers. If you go this way, be prepared to spent alot of time to get it right. Look at the post on this board, you will find a problem post every were on these Hobby controllers, and stepper, step servo drivers. As they say, you get what you pay for.