If you have your air conditioner running, it's going to cost you .. no way around that, however, there are a few things to do to keep your air conditioner at maximum efficiency:
Keep the AC away from sources of heat, such as lamps
Keep windows closed
Opt for open windows at night instead of using the AC
If possible, set up your AC in a window that is not in direct sunlight
The two best ways to save electricity on space cooling is by reducing the temperature and insulating your home.
Each two degrees (Fahrenheit) higher will save you 5%-10% on electricity.
take a look at http://funadvice.com/r/151jq7v011v and find more ways to reduce your space cooling costs and save some money.
Hope this helps.