Yes l understand. Same with my vt.
When saying new hvac, you mean used?
By taking it out yourself, finding out whether you can fix it or replace it will be cheaper. Then refit it. Your only up for coolant. Get the heater going, then get the a/c going later in the year. Before starting, ask the people who gassed the a/c, if they degas it, how much & then regas it later in year, how much. Ask a few places & explain what has happened.
With what the guys are saying in the other thread, l suspect its one of the hvac doors or vacuum hoses or actuators. I believe the vacuum tank is under the inner front guard
When taking out the hvac unit from under the dash, l put a bypass hose in at the tap, so as l can still drive.
Anyway good luck with whatever you decide.