What's largely at risk is the framing, insulation and drywall.  

You'll likely also need fiberglass insulation boards- add $100 per square.

Considering that it would likely take you ~10% in transaction fees to sell if your plan to rent for cash flow does not work out, then it is highly likely that you are losing money on that deal.If, on the other hand, you are able to buy under retail market value and force appreciation in the short term, then not only does that help your cash flow by getting into the same property with a smaller investment, but it also insulates you to some degree from short term market fluctuations as well as gives you another viable exit strategy to sell at a profit if you need or choose to.Ideally, if you get a good enough deal, then you should be able to sell at profit (even after transaction fees) at anytime from the day after you close escrow, to the day after you finish rehab, to 10+ years down the line after holding as a rental.

Plus add in studs, drywall, insulation, door and paint and figure roughly another $1000.My partner/fiancee is a pretty fair carpenter so she did the walls, drywall, painting, etc. so we saved bucks there.IMO, a full bath is far superior to a 1/2 if you have the roomGood luck.

Had this discussion with one of my clients yesterday.....a few things....one is sewer pipes...at this point I would probably be looking to see if they were replaced...in my experienced the cast iron black pipe lasts about 50 years...occasionally 60 or 70...at this point you may be looking at also replacing electrical and plumbing systems and insulation.    

I would check to see if their is any insulation in the attic and crawl space first. 

Horsehair plaster, poor insulation, crappy windows, 2×4 sidewalls...

My general estimates are at least 10k for the crawl space clean and insulation and probably another 15k on the roof.

He wanted every trace of the wire removed, they could leave insulators but no wire.

Had to pay to have insulation from under the house removed $2k (it was vacant for 18 months so rats were in there etc)8.