I have heard that a new a/c with duct work is 15k for a 1000sf house.

For example, if the house has a crawlspace, I don’t usually recommend a duct scope because the inspector can view the ductwork under the house.

The scenario is I found that the duct work in the crawlspace of a single family home I have under contract needs to be completely redone.

Ductwork can be assessed from the crawlspace.

Could have a gravity furnace, poorly laid out and insufficient ductwork...particularly cold air returns improperly sized.4 - Plumbing. 

Have your AC contractor show up for the inspection to advise on what might be problematic for them in installing the duct work and get a quote.I deal with these older properties - both residential and commercial - everyday so it's less of a threat than a "don't lick the walls and don't snort the siding."   

Anyone have an investor friendly contact to do flex duct work?

The most expensive part of adding forced air to a house without it is the duct work, followed by the actual air handler and compressor. 

My cousins had one of those in an addition that they didn't bring out the duct work for.

We took a look at the house yesterday (entire block was closed off from traffic for the clean up and dumpsters, etc), and not only is the electrical panel cover rusted, but I am sure the HVAC ductwork/furnace/water heater were also all submerged, along with the central AC condenser outside the house.