How much would this cost to build?



You'll be lovin that place till the next Hurricane Katrina blows through and leaves it completely underwater. Sure the stone will be standing, but you wont have a window left in the building.

What is this...and island for ANTS!?

LOL. Ft Jeff is probably pushing a couple hundred years old. No windows. Fairly sure glass wasn't on the material list in the early 1800's. Lots of hurricanes since then. Other than the waters cloudy and boat debris it looked the same to me a few days after both Georges and Wilma. As far as the size of the place, on the left of the pic there is a Hatteras sport fishing type boat at the end of the dock. That is probably around 70 feet LOA to sort of give you a reference. Inside the Fort walls is several acres and those double walls are probably 8 to 10 feet thick each and a good 50 feet high or so. The openings on the exterior two sides closest to the camera, some of those are car size. It's quite a place with a really cool history.

People have holed up there during hurricanes on purpose if they couldn't make it to Cuba or Key West in time. I imagine Ft Jefferson and the Dry Totugas will be there a while longer.

Pretty good diving.
 
Figure just the island will cost you between 10-30 million depending on the location and features of the island. Is there reliable water available? Is there a sheltered bay? What quality sand are the beaches made of? Are you close to a drug lord's island?

Take the cost of whatever building you're planning on putting together. Add between half and double that cost to the total cost of building. You're paying for transport of materials and challenges that will inevitably rise due to the proximity of the sea.

You will also want to hire a caretaker. Maintenance on an island residence is a bitch.