The key is lot size and opportunity to add on another room esp in pricey neighborhood at exit.680 sf is adequate so may be add a porch later.

To see if you are on par with others, do a search in the area for a rental of the same size.

I have it on the market for 3 mil .in development you have no value until you have a user.. unless your going to develop it yourself.and if its just two residential size lots those would have very little value unless they were needed for a greater good.

Best bet is to get some off market deals. 

We are looking for a cloud based (hard wired) security system for a mid-sized apartment building.

Disadvantaged to be aware of include fire and life safety, increase in structural support, difficulty in construction logistically.Your best bet is meet with a local GC.

My short answer to you is, I would expect about a 50% occupancy rate and probably not more than $200/night ADR (average daily rate) depending on the size, quality and location of your STR. 

If the same name keeps coming up I bet they are worth looking into.  

Garland is a great bet that fits your two criteria.Blue collar, many trades workers there who service the rest of DFW.

@Sviatoslav Gulko  sounds like the ductwork was sized just for a heating system .