There seems to be a lot of cheap second hand satellite dish actuators around one ebay these days, with people setting up manual pc controls.
I saw one guy using an old battery drill with some all threaded bar stuck in the chuck and a nut secured to the mirror board for a linear actuator - now thats a cheap solution.
I've been working on a cheap pc driven one using an old laptop inside my shed, with one of these to control:http://www.pololu.com/catalog/product/1350
and six of these MG996R metal gear servos:http://www.hobbyking.com/hobbyking/stor ... oduct=6221
To give me a total of three smaller lightweight mylar heliostats that I can fix to my shed wall, and remotely control from a second pc inside my house.
Nice idea to mount your driveway reflector on a gate - you could swing it during the day with an actuator...