In california PG&E has a website that you can go to and they have rebates and such maybe you can apply for an energy star loan through a contractor who does the upgrade. I contract and do this exact type of work but I am in the Sacramento area too far to help you. Heat pumps can be efficient I believe that they have up to 14 seer heat pumps. The higher the seer rating the higher the energy efficiency. If its at all possible natural gas or even propane costs about one third what electricity does. Pay back depends upon usage of course but with an energy star loan you can make low monthly payments. Good Luck