Especially if it has been vacant, you may need to re-apply for a Certificate of Occupancy (CO) which entails a building inspector coming out and checking all of what I mentioned. 

The approval process, what it entails, and when it would make more sense to get a HELOC rather than a refinance?

I am probably more apt to stop them from buying if I am being truly honest, because I know what that "new kitchen" or "opening up" is really going to entail and cost. 

They rely on agents, contractors, inspectors, and lawyers to "do their jobs" when they don't have the foggiest notion of what those jobs entail (nor do they have any real respect for those jobs).

And while I wasn't doing the work, I got a good understanding of what was entailed at a high level, because investors will ask about it.  

That's a solid point of view to see what the problem really entails 

If it was then he should have a line item bid and price for all of the work entailed therein.....slab/foundation/framing/insulation/electrical/siding/drywall/paint.

I want to start small to build up to the more complex things that this business entails.

Another reason the range is so wide is because contractors wont really know what kind of work this project will entail until they see behind the walls and look into plumbing, moisture issues, electrical, foundation, etc. 

Mind if I ask more about your system and what it entails?