Was it on the ductwork? 

Adding to what others mentioned, it could also cost more if there is plumbing and duct work on those walls (someone already mentioned electrical). 

However as I understand it, the fittings don't restrict flow as much as would be assumed by first glance and it's sort of calculated similar to air flow in duct work.... a 90 degree elbow fitting can be roughly accounted as the same as x ft of straight run in terms of how much pressure is lost.

This is for the unit only, not sure about duct work.

White cloth tape at ductworks, mastic, 9x9 vct tile are items to look for that contain asbestos.

We have done ALL the work ourselves except for finishing the drywall.I will do a whole RENO thread once its done, but here is just a quick overview of what we have done.Whole new Heat and Air unit, switched to gas, and moved duct work from under the house to the attic.

They'll be "investor friendly," but likely nobody I've used in the past.For the most part, this is what we'll be doing to both of them (with estimated budgets):-  Lead inspections/clean-out/permits:  $1000-  New plumbing (and new fixtures):  $6000-  Upgraded electrical (and new fixtures):  $5000-  Install forced air heating/AC (ductwork and units):  $7000-  About 50% new sheetrock and paint:  $5000-  Flooring: $2000-  Cabinets/countertops:  $4000-  Replace doors/trim as needed:  $2000-  Appliances:  $1000-  Exterior repairs as needed (doors/windows/etc): $3000-  Misc:  $1000TOTAL:  $37,000 +/-I've done literally a 50-100 rehabs of this exact scope, though I've never done one for a rental unit. 

The water damage destroyed all of my downstairs drywall and flooring, bathroom vanity & cabinets, most of my heating ductwork, etc.

Depending on how big the house/condo is, split systems can be a good route as it allows for you to skip the duct work.

If not, could you put the furnaces in the attic and have to run minimal duct work (duct work is usually easy to run in an attic)?