As far as what it costs to fix to that level, I wouldn't know fully without seeing the house to know all of the details (mechanicals, layout, etc).

I had a vendor get in major trouble in Jackson doing this.. so I set up a transactional funding mechanism for him.   

No opinion on your location, but in general:Older homes:Better framing/worse foundations/mechanical systems in need of serious update (electrical, plumbing, heating)/area either more run down or more expensive (already gentrified)/more compartmentalized layout (no "open floor plan")/more dangerous material (asbestos, lead paint, knob & tube)/more termite damage/cheaperNewer homes: more or less the opposite. 

Reached out to other insurance companies and said they would but would have to transfer my homeowners and auto, which I don't want to right now.

I understand it wasn't a great deal for them but I was trying to make them whole.Today, they put a mechanic's lien in my property, just as I'm getting my first tenant in.

The mechanics of the contract for renting the land and selling  the MH simultaneously means potential complications if things go awry. 

I also believe it helps to be the FIRST agent to call, so set up auto emails or check zillow FSBOs a couple times a day.

What you're considering might be a great idea or a very bad one.For the record, the exact mechanics of rent-to-own (really, lease/option or lease/purchase) vary from state to state.

I am involved in the rehab of a fire damaged, three floor, six unit building in Worcester, MA and am looking for referrals for structural and mechanical engineers to support this project.

Dan and Brandon gave you some very good insights into the mechanics.