A better idea is to get an inverter, that's about 250 to 300 USD, that works for like 4 hours with quite a bit of electrical domestic equipment. So the ides is to have it just for the rig and not the other electrical equipment. Then connect a simple 1200VA UPS to it and then the rig.
So incase of a power failure , you have no system shutdown for atleast a good 6 hours. And in todays time of technology, I doubt a place that uses an i5 3550 and 16GB of RAM to have a power cut for longer than 2 hours.