I always take out legacy systems and put in ductwork and high efficiency direct vent lp/gas setup with AC.

What does it cost to ditch the window units and install an HVAC unit from scratch...all the duct work will need to be built and placed?

Here in Florida, about $8800 is about right without any duct work. anything higher seems way out of line

However, the ceiling is unfinished and has exposed wires not in conduit and ductwork running everywhere.

 $300 was probably way too generous but I have a soft spot for a young couple with kiddos that are working hard to make it.I had a HVAC change out on another unit, duct work in attic fell apart on the install and the unit ran all day and night from Friday afternoon until Tuesday when they came back to go in the attic and fix the duct work.  

That $250 is primarily used for cleaning out duct work and any other odds and ends that need to be touched up.

I know those are kind of ramble-thoughts, hopefully they make sense to you.I got baseline quoted an HVAC replacement of $4000 (inside and outside) per unit, this isn't including ductwork and not knowing the interior.

I know they are less efficient than the overhead fans but this house was installed with one a couple decades ago.For going with a range hood, the cost is $200, installation is $500... which is fine, but ductwork will have to be put in and creatively.

I inspect attic and find 40 year old ductwork and places where there is no insulation at all.

That might explain why there is no ductwork for the AC.