My HVAC guy keeps telling me to install a couple of heat pumps (he doesn't like driving out to me), solar panels, and an in-house battery; what sort of complexity was this job? Are there online sources you used?
You can also gain quite a bit by just fixing drafts and putting in proper insulation. Which can be much cheaper to do. I also had the guys go thru and fix an leaks in the duct system. That way the air was coming out where it should. It is amazing how badly that is installed many times. I also had them put in an attic fan which vented the attic when it got to about 110F. Insulation would have helped more there and I screwed up and put it off. If your house is older than 2000. I say go thru and review the existing insulation and look for drafts first.
It trimmed my bill from about 350 a month to 200. My new house has excellent insulation the house is slightly bigger and the power bill is in the 80-150 range (less because I got solar, but I figured out the actual cost anyway). It has one unit and an air valve to switch between the floors. So the total cost is lower but the one unit will run longer. That savings I am getting is mostly because of better insulation.
The only thing that might catch you up is designing the system and ensuring you right size it for your heat load requirements. I'm sure you could research this pretty well, but your HVAC guy might also be happy to consult on that portion.