Another option that would be a little more work (and involve a computer) is some sort of X10 protocol
based equipment (or other home automation protocol like Insteon). You could easily program the computer for any sort of on/off intervals you wanted. It might cost a bit more than $20, but definitely not the $170 you found in my previous link.
Again, it would require a computer, but that could be anywhere in the house as the home automation gizmos use power line and/or RF communication.