Does this exist in the nashville area? 

I personally would spend an afternoon and reach out to different local lenders (banks and credit unions) and see what they will offer for a HELOC or possibly refinance the existing loan if your rate is high.

Maybe you're not and I'm just unclear on this, I just don't know of a county website that exists that's at a government level like this that offers value margins other than for property tax assessment purposes. 

A shortage of employees can produce a variety of negative effects, hindering the ability to grow and expand, or even to meet existing staffing needs.

An RV park came to mind as well as there are existing slabs from the previous mobile home park that was there before it was forced to close due to the flood plain, but I am not sure that it fits the local demographic for that area where the land is located as I don't see many of the locals having RV's to park and store.

And construction loans are going to want a larger down-payment (i.e. 20%) versus only needing maybe as little as 3.5% to purchase an existing MF property where you will live in one unit and rent out the other(s).And a construction loan to build a MF property may be considered commercial development (even at 4 units) versus building a SF home to live in yourself - and if so, they may want you to have prior rehab / development experience to some degree.

I noticed that many towns/cities doesn't allow STRs and existing ones might be functioning illegally.

So rather than "guess" at the price, get an estimate or two.When you are paving asphalt over a gravel road, you are talking about a "from scratch" job, as opposed to adding an asphalt overlay on top of an existing asphalt surface.

People think I'm a Portsmouth basher, but the fraud that exists in every level of their government is for real. 

@Gavin Welch Cozy has been shut down to new users for months and all existing users are being transitioned to Apartments dot com.