Here is some information about the cabanas there that another CLF member, djgifford, posted on another thread. Unfortunately, it doesn't include the price. I'll see if I can fing that nexr.
I got some information from Carnival's site....

Relax in the shade and comfort of your own private poolside cabana at Grand Turk’s Cruise Center.

On this excursion you will:

• Stroll a short distance from your ship to Grand Turk’s Cruise Center (adjacent to Jimmy Buffet’s Margaritaville Restaurant and Bar).
• Take in the beautiful view of the magnificent swimming pool and ocean, as you relax in comfort in your cabana, complete with an outdoor shower and private waiter service.

Note: The cabana can accommodate up to four guests. The cabana rental rate is per cabana. Only one guest need purchase the reservation for the group (maximum 4 guests). Cabanas are not air conditioned, but have ceiling fans and a window that can be opened to let in the breeze. Guests must be able to climb three steps to access cabanas.

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