A neighbor of mine uses screen door pneumatic springs in his Halloween animatronics displays. If you remove the "adjustment screw" and screw in a brass fitting, you can hook that up to an air compressor and electronic valve (sprinkler valves work great). Activate the valve and the air moves the actuator. Turn off the valve and the system bleeds air at a slow enough pace to drop the actuator back into position.
This makes a very cheap, but not very precise actuator. Good enough for what he's doing and he can get replacement parts at any hardware store.
I bet you could find instructions on how to do this on the internet.