Dry Tortugas camping (for up to three nights) is offered on a first-come, first-served basis. This is primitive camping at a National Park - you must bring your own equipment, food, and water.
Campers can access the Dry Tortugas National Park via high-speed ferries departing from Key West. 
Cost: $175 or $180, depending on which ferry you choose. 
Ferry Schedule: both ferries depart Key West at 8:00 a.m. (check-in at 7:30 a.m.), and return at 5:00 p.m. 
Reservations: Call 877-463-6539 or click here.