Simular to the install of a generator. I would say 1200 to 1500 depending on mounting configurations. Is your box insulated? If not, there is a major cost there.
For under the box units, I like the Carriers. For upper box mount, I like Thermoking. We have had both and I like the upper ones better. They don't get all the road chemicals and develop rust on them so quickly. But....they are a pain to perform service on.
Leave that to someone else.
If looking at quietness of units, Carrier seems better.
Davekc