Investigate AC alternatives
Consider a whole–house fan. If you live in a climate where it cools down at night, you may benefit from a whole–house fan, which pulls in cooler air through open windows and exhausts it through the roof. Use a professional contractor to install it.
Use an evaporative (or swamp) cooler. If you live in a dry climate, consider an evaporative cooler, which contains water–saturated pads that cool interior air by 15 to 40 degrees (warmer air gets pushed out of the house through open windows). Evaporative coolers use less than a third of the energy of central air conditioners and cost about half as much to put into place.