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

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.

It would have been very expensive to replace all the ductwork in the house (undersized for A/C) or to add 4 mini-split A/C units.After seeing another house across the street sell for $199k (a great comp), I decided to sell.I will be rolling these profits into other larger deals, most likely, outside of (the very blue) Maryland.   

When the home was being rehabbed, the city did not allow the contractor to put any duct work below the second floor.

Things like ductwork (for HVAC supplies and returns), and plumbing (water supply and waste pipes as well as vent stack pipes, and then there could also be radiator pipes) - just for a few examples.So, you should determine which of these might be there before poking a big hole in the wall (like they do on the TV flipping shows).

When you say this house never had HVAC, then you should find out how much installation of ductwork will run from a local HVAC contractor.

I went and seen it today. 1/4 of the rear fascia is gone, some of the soffit has vegetation growing on it, the shingles looks “okay”, the wood under the shingles are planks, the crawl space in the attic is very small, the air handler will more than likely need to be replaced, because of mold concerns I would budget for the duct work as well, but I would wait for the a/c guy to look at it.

Higher efficiency, fewer problems, etc. but in your case, maybe a few hundred $$ can fix the panel and ductwork?

OK:http://www.deq.state.ok.us/lpdnew/MethLabs/meth.ht...Seems like you need to air out the property, then maybe close it up and turn off the AC for a few days to get any remaining volatiles to evaporate, then air out again etc. and clean all surfaces and the vents/ductwork.

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.