I keep mine at 78 (F), my average electric bill for my 1650 sq ft. home is $145.00 a month (includes a/c, cooking, hot water and clothes dryer). The air conditioner does not make the air colder, it pulls the humidity out of the air, so the only thing that happens when it's set really low is the evaporater coil freezes.
The weatherman told us tonight, that the temp was going to go up, so we'll be experiencing severe condiitons just like the Southwest has been experiencing. So far it's only been getting to the mid 90's here Florida. However, I'll take the heat as opposed to the hurricanes!