That seems like a lower demand area than any place I would ever invest.   

Some of the costs quoted shock even seasoned flippers as they are lower than even material are in many markets. 

I will continue to do my research and try to find a CPA that handles Texas and has a lower minimum I think.

Airbnb listings (newest to oldest)(Hit a snag in lower reviews haha I promise I'm a great host): airbnb.com/h/familydelightairbnb.com/h/homeoasisfloydairbnb.com/h/sereneoldtownsantuary@Sarah Kensinger@Ika Sargeant Well done.  

If I have lump-sum free cash, should I just apply it to my mortgage to recast so that my monthly goes lower?

I'd assume all vanities, lower cabinets, 3to 5ft of drywall and base will all need replacing. 

They may tell you a certain % but then if you offer significantly lower they might change or retract that number.

I have lower-end property in a small town.

The buyer can obtain a property with no mortgage qualifying and or a lower than current interest rate, or on terms not readily available otherwise.  

Your main concern should be whether these bedrooms and bathrooms on the lower level are legal and have the proper egress require for fire code and livability.