(I imagine this would depend on a number of factors, but I’m at a loss on what to compare a USDA-guaranteed offer against.)

I assume your agent ran the CMA on the property and if so, did you guys did compare it with other 3 bed rooms, 1 baths in the area? 

Comparable houses to this house are selling for about 75% of the list price while similar size land plots within a couple of miles have sold for 100% of the list price. even after commissions and whatnot, it looks like a 150% ROI is realistic in just a couple of weeks.

Payments are too high compared to rent. you're over $650 per month before maintenance, property management, capital ex reserves, etc...

It's a completely different process for appraising, loan origination, and ownership structure between residential and commercial.Commercial is based off income the property produces, residential is based on comparable nearby properties.

Compared that with San Antonio (like areas around 1604 ring), where you can get much better houses (newer, cheaper), but with low rents too, because there are so many. 

Your problem is that you may have trouble securing traditional financing because of your debt.

The price per unit simply allows you to compare it to other nearby sold properties. 

Certainly affordable compared to market rate, but still not quite affordable by federal/governmental standards.

I took the class, passed the exam, got my license, and dove in head first into traditional Real Estate for about 6 months and didn't close a single deal.