How much should I estimate this will cost? 

If the market value mentioned above is accurate and the “initial” loan balance hasn’t increased by rehab funding, I wrote above that the proceeds are just a couple million after closing costs and commissions.

Generally there are multiple units for each "zone" if you will when I've seen them installed.Regarding your problem at hand, I personally would simply adjust your plan to move and make your initial plan to get the current issues resolved, while costly now, in the long run holding onto the unit will likely pay off. 

May not be your cup of tea but they are cost efficient and they work to add passive income at a fraction of the cost to build a SFH.There are a few "Tiny Home" builders in Tampa and Manatee doing a ton of business.  

Now a-lot of times you buy a home from someone with seller financing and they hold the note for 6 months to season it and then sell the note to another investor or a firm and then it will most likely show up on your credit because these are more sophisticated investors.In regards to the benefits of owner financing you won't have to pay closing costs to a bank.

Here's an article with FAQs including the cost of a study.

You can usually get a lender to go 85% of cost or 70% of the As Completed Value for such a project.

Hard Money will usually finance 90% of your purchase price and 100% of your repair cost up to 70 or 75% ARV (after repair value).

Cost $5,000I sent out 500 post cards on several occasions that I designed and bought two houses.

Of course it isn't going to work for everyone...then again, I also have many friends with degree's that cost them 6 digits that cannot get a job in their field!