If there's ductwork, it's something being installed into the building that has to pass inspections. It's not just one or two holes in the walls that need to be sealed.
The new heat pump system cost roughly $14,500 and provides heating and cooling via ductwork that was already in place.
(In a more enlightened world, I think that a system with the refrigerant fully contained within the outdoor unit that uses plain water as the heat exchange fluid could make a lot of sense, and this would not change the pipe situation.)