I live in NE ohio in Cleveland suburbs.(not far away from western PA). I don't get discounted electric. I have a 90% natural gas furnace and just replaced my A/C with a 15 seer heat pump. My electric costs .11 total cost delivered per KW/hour. My electric isn't cheap but not crazy expensive. Even with gas being pretty cheap this season, the heatpump is less expensive to run. I run my heatpump when above 25 Degrees. Sometimes I'll switch to auxiliary (my gas) if there is a blizzard and the heatpump goes into defrost alot. The advantages to the heatpump with having a gas furnace is that you can heat with the least expensive option. If gas gets crazy expensive again, just run the heatpump. Its also nice having another stage of heat. When running the heatpump you don't have any cold-spots that you might get when running a single stage furnace when its not very cold. Also, a heatpump system shouldn't cost much more then just replacing a regular A/C. If it does, the installer is charging a bunch extra beyond costs of the components. My heatpump system requires a fancier thermostat. I would go with honeywell wireless focus pro. It doesn't cost a ton and it does a great job for dual fuel. Its also easier for the installer too. The heatpump condenser itself only costs a couple hundred more than a regular A/C condensor in my experience. 9 grand sounds like alot. Call some independent licensed installers and get a rough estimate over the phone for what you want.

There is a major problem with that system. Not enough info to determine anything of value. It takes 5 minutes to reach a decent cooling level Efficient operation zero! You need long run cycles NOT short cycles udarrell - 2007

Fahrenheit: solar powered HVAC sounds really interesting but will it be adequate to heat a 3600 sf house (website seemed to indicate 600 sf.Right now, you will not even be able to purchase from them as demand as far exceeded supply so they decided to sell commercially with their largest customers being the US Navy and McDonald's. But, the HVAC world is changing with installation demands requiring more exacting and educated installers; the tradeoff will be better results and an industry in change (it's about time). Since you are in Southern California I would also consider a Energy Recovery Ventilator for those many evenings where you will only need fresh circulation and no need to run the HVAC. Link is for information reasons only and not a spec: Energy Recovery Ventilator

Is the main system located in the basement I assume? If so, that would be difficult to run ducts, but often times they can be run through a closet or wall chase. I'm not sure if you could do the in-wall unit without having it exhaust outside to allow it to work properly. Hopefully someone else can give you better advice for this particular situation, but I would say running ducts from the central system (return and supply) is the best bet. Have any contractors come out to give advice?