If they’re replacing a boiler in a hot water system it can either be a bit more expensive or a LOT more expensive. If it’s pumping heat into the water it’s not so bad. But if you have to run duct work or put up a bunch of mini splits costs start going way up.

But if it’s a hot air system it shouldn’t be much more than adding A/C, and if it already has A/C it’s just a reversing valve.