Check the age of your current heating/air conditioning unit. Newer products are much more efficient than older ones. Current furnaces on the market are over 90% more efficient! Modern air conditioners also use much less electricity than their predecessors.
Also, be sure to check the SEER or Seasonal Energy Efficiency Ratio on the product you are considering. This efficiency measurement is similar to Miles Per Gallon for cars. The higher this number, the more energy efficient the system is. New units have SEER ratings from 13 to 20+.
Have you heating and cooling contractor do a savings comparison for you to see which system is the best value.