The contactor box next to the panel seems to be about as easy and cheap as it gets. It is very portable and only takes about an hour to remove and install at the next house. They switch 6 single phase circuits with the ones I have seen. That is plenty to have enough lights on to give the house a lived in look. You certainly don't want to be flipping the main. That would turn off the HVAC and refrigerators. (think: mildew and broken icemakers)
