There are several different ways to help with cost:
Install a programmable thermostat; this will help reduce the work load of your system while you’re not home.
Replace your incandescent light bulbs to compact fluorescents (CFLs) or LEDs, which are more energy efficient.
Use a ceiling fans, when you can, instead of your air conditioner to cool down
Make sure your windows and doors have good seals, so they are not letting air out.