Around $35 in winter and $75 in summer for 388 sq ft first floor apartment in the shade. When I was being super-extra careful and did not have an at-home Internet connection (and went to work for ten hours a day, minimum), I managed my fridge well (large stocks of just-in-case water with space for airflow and a good seal) and the weather was temperate, it would average $11, lowest being $3.33 (not sure how that happened). Of course, now I pay for two houses, one of which is an A/C addict (they were proud to have turned the thermostat UP to 72, even when no-one is home), and that's around $150.