I would like to include this expense in my flip calculator as accurately as possible so as to not underestimate this potential problem.

The danger of posting in a public forum is that you will get lots of opinions but not always informed, accurate and useful responses.I agree with @Jay Hinrichs.The primary issue at hand is that you need a seller who has capacity, power and authority to pass marketable title to you. 

The other is gamble on the open market and maybe get $85k. 

Gamble / Play the lottery3.  

So add points on top and you should be pretty accurate.

@Ndy Onyido   Nothing is certain, everything is a gamble.   

But its a gamble.

However, for accurate, useful information, walk the house with your contractor, foundation person, HVAC person, etc.  

If 35% of what you read is accurate, it's a lot.

@Ed B.First think is, I'm no expert, but Ideas I have plenty of them :D  Take them with a grain of salt.In your post you have an assumption that I believe is not accurate...