But they are not going to go into detail about which walls are load bearing or not, which have electical and duct work in them, all of which will greatly impact the cost to implement their design.And if you want full service design to actually account for all the issues that will actually arise, you are likely looking at 20k+ for design work + 5-10% of total rehab cost. 

I agree with the others about a minisplit (similar to a heat pump, but doesn't require any duct work). 

AC is a must and will require duct work or minisplits at large expense.4.

This doesn’t include any needed ductwork (TBD).

If you have ductwork thats one compressor and condensor unit.

I never tried to save the duct work though, all have needed new HVAC with duct. 

I will say though if you have duct work in place already replacing existing system tends to be most efficient route. 

But we have also added central air to house/apartments where the heat is hot water and have installed all new ductwork. 

You can easily burn up more labor reworking the ductwork than system install, which is really plug & play.

I recently had a HVAC unit installed running duct work and that alone was about $18,000.