There are several new developments (luxury apartments over retail) going in downtown. 

We are working on a development project that would include building single family homes preferably luxury.

Sounds like you're aiming for a major rehab at a high ARV (luxury stuff).

We have had vacation rentals by the beach, close to downtown, luxury homes, you name it. 

I wouldn't under take that either unless i had my own cargo planes and ships leased out with a work permits and housing for a US crew.I have owned businesses and built commercial and luxury home properties in Turks and Caicos and the Bahamas. 

Our new STR is in a location where AirBnB/Vrbo does not collect lodging taxes on our behalf. 

The letter states In the unincorporated areas of South Padre Island all lodging businesses and private home vacation rentals must collect and remit Hotel Occupancy Tax.

You should think of property management as a luxury that you can't afford right now.If we had our 37 units under property management it would cost us over $50,000 a year!

My new luxury pool cabin with a view is on pace for amazing numbers this year and I’m in the process of building another one.  

I would say it's between 15-50k, really depends on the position of the complexity of pipe, electricity, plumbing, permit/no permit, framing and how luxurious it would be, etc.