Everything points to those zip codes being "undesirable" areas even though, I would not call them "hoods" like you may see in bigger cities, more like low-income, majority African American areas, some of those lots have been on the MLS for over 5 years, so very low demand.One thing about Alabama is that, there are huge variations from city to city- Montgomery is not a desirable city,  Birmingham is going through some gentrification where you have homes in the 20-30K and 200-300K ranges in the same zip code.

And today I walked by a Nissan variation.

I've calculated it anywhere from 6% to 11% based on management fees (or self-manage) and a small variation in rents (from $2000/month to $2250/month).Thanks for your input.

As expected, there are slight variations in the managements fees and many clauses, but the differences in termination fees, mandatory commissions, and willingness to negotiate were surprising and could have a huge impact on exit strategy when the time comes. 

or some variation of this?

The major issue is the permit process, and sometimes variations between various cities and jurisdictions on their particular requirement.

The most common variation on this theme is an assumption in which the buyer takes the property and any existing notes “subject to” and executes a subordinate note for the seller’s equity.

Generally embedded with some variation of a PPP, so consider your time horizon and exit strategy. 

I would suggest building a relationship with a real estate agent in the area you'd like to purchase and get their opinions about dynamic variations in different parts of cities.

You can still use variations on this, say apply a 1.3% rule.