The fire itself may have been contained to one room, but you will need to look at the ductwork and smoke damage in other areas of the house. 

@Harrison Vann To answer your original question we recently paid $6,700 for complete AC on a total gut rehab, 100% new duct work/vents and AC unit.

Generally you want to take care of things inside the walls first (plumbing, wiring, ductwork, insulation) then drywall/paint, then cabinets/vanities, then flooring and trim.

The basement is partially finished, but the big pieces I need help with are updating a half bath to a full bath (add a shower), turning a dry bar into a wet bar (adding a sink), and moving bit of hvac ductwork.

Im looking at my furnace, and I see which way the air is blowing....based on the direction of the filter AND the fact that the filter air arrows are pointing towards the furnace.BUT...when I follow the ductwork, it looks like the air is getting sucked in from other vents that should have air blowing out of.It looks like this: AIR VENTS <- FURNACE <- FILTER <- DUCT WORK <- AIR VENTSThat makes no logical sense to me.

If I redo the whole roof and duct work for central heat/air.  

It is a great secondary heat source in homes for sure, and I actually have added it in my own home as a secondary heat source for a room that didn't have duct work.

I have a single family rental, which had updated plumbing about 20yrs ago, mostly copper, but the silly do it yourselfers have several occasions where that copper is touching steel duct work and other steel.

furnaces are an easy swap when not doing any ductwork and it really gives the property a finished feeling to the end buyer when they dont have to question any of the mechanicals.Did you work with any real estate professionals (agents, lenders, etc.) that you'd recommend to others?

Has a dated (boiler/baseboard) HVAC system (no ductwork, but enough copper piping to sink a ship) and old solar panels but no aluminum wiring, the hydro pipes are copper, drains are cast iron.