You also mention the low fee of $50 / month for HOA fees and though it may look very cheap on the surface, you have no idea how the communities financials have performed over the last few years and you may have HOA fee increases annually.

Manage them yourself, go to court yourself and fix them yourself and/or use a cheap handyman.

Or can you pick up some additional contiguous land for cheap, and put your retention basin on that land?

The numbers look great for cheap houses and rents and they wanted some data on the area.

Here's an example I used many years ago:"I'm interested in a cheap fixer-upper single-family home under $100,000.

At some point early on you will have to pull the trigger and have them do the work so they see that there is a symbiotic relationship.This used to be true, but nowadays you will just lose out on a lot of really good and talented GCs who are tired of being told - "hey take a look at this house for free and I'll give you a lot of work in the future....as long as you work for cheap".

That being said, good things aren't cheap and cheap things aren't good. 

I don't say this to sound mean, but you need to decide if you're running this as a business to make profit or as a cheap housing alternative for those in financial hardship. 

Crazy cheap. 

The cheap homes look good on paper, but cost a lot more as they often attract less desirable/more problematic tenants.