$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. 

@Tom DohertyWith new duct work around $6k, without duct work $4k

Assuming the ductwork is fine and assuming this isn't a 5000 sq ft mansion, you can get a new unit for around $5500 including a new furnace. 

I'm no expert but that sounds like a $8k - $10k job if you need to run duct work. $3k - $5k should cover a single unit with a lot of capacity.

You can always offer lower on the property factoring in new furnace cost, instillation and potential duct work.