$25, but we live near Seattle so it's not really hot in the summer and we use candles instead of electric lights most of the time since it's nicer, softer and encourages earlier bedtimes
We get candles at Six Star and yard sales and thrift stores. We got enough candles to last us for two months for a dollar total at a yard sale a couple weeks ago
ETA - In the winter the bill is pretty much the same because we don't use our electric heat. We use the woodstove instead and get maybe a cord of wood for the whole winter since it doesn't get really cold around here either.
love and peace.