This is the motorized lock I have built for Hackerspace Brussels.
It is still work in progress, but i wanted to know if the salvaged parts and my mechanical design would fit the bill. Total cost so far: 31,24 €
The lock is a standard lock with key outside and a simple knob inside. The knob is held in place with a screw that can easily be removed with an Allen wrench. The shaft is round with a flat. I was just lucky to find a pulley in my junk box that was a perfect fit.
The belt, pulley and stepper motor were ripped off an old fax.
No arduino, no microcontroller, just pure glue CMOS logic driving MOSFET transistors. :-)
Project page: https://hackerspace.be/Doorlock
Build pictures: http://gallery.askarel.be/main.php?g2_itemId=48006