Take a look at the following forum:
http://www.kolor.com/forum/Half way down the page Panogear, Merlin, Orion, Papywizard section.
The guys have modified a motorized equatorial mount for photography. Listed in the forums are some contacts for purchasing the equipment at a good price.
The last time I looked the Merlin/Orion mount cost about $US150. Even if you don't purchase the mount, the electronics used may be of interest.
If the costs are too expensive try modifying a cordless drill motor and couple that to a windscreen wiper gearbox.
Cordless drill motor hack:
http://www.wa4dsy.net/robot/drill-motor-hack
