About a year ago I added a power feed to my mini mill. Saves the arm when doing repetitive tasks. It runs at about 10 inches per minute which is fast enough for me. Cost was about $50 total using on line components.
The motor is the jewel of this system. All Electronics has them for $17.95 each. Surplus car seat drive motor that is rated at 180 rpm. The lead screw adapter could have been turned on the lathe but for $8 I just ordered it from Little Machine Shop Part Number: 2546. It fit my mill perfectly. I may have had to bore out the end for the motor shaft but it worked perfectly. I did cut the shaft for a good fit on my machine. Just use an abrasive wheel grinder for that. Ground a flat on it for the coupling.
The engage/disengage is a manual affair. Just move the motor/shaft coupling to the inside hole on the motor mounting plate and rotate the lead screw just a bit to capture the pin and it is engaged. When no longer needed just relocate the motor to the outside hole and it is disengaged.
The power controller comes with a switch and pot for speed/direction control and that was a bay purchase.
Power supply is rated at 15vdc and 5 amps. Mounted that in a mini box with a clear poly carbonate cover so I could see the led on the power controller.
Oh, yea, the motor mounts to the motor bracket with a pin that can be seen in the pictures. A set screw would be good to secure it but mine has never fallen out.