This post started out with the premise that other home automation systems are too expensive. Aren't X10 systems pretty cheap ($99 for controller and software)?
One issue with X10 is that they require a computer with X10 controller on 24/7. The computer provides a web interface and can turn devices on/off at scheduled times. For example, you may want to switch an outside light on automatically at 7 PM every day.
Have you given any thought to a server solution, i.e. leaving an android device at home and on 24/7 that can be connected to remotely?