There are regular taxis that go over to Atlantis from the port terminal. And in the past there were also water taxis, but I am not sure if those have restarted or not. The water taxi waits to fill with lots of people before it leaves, so you would not be traveling alone. If you take a regular taxi, it would just be you in the car. Make sure that it is a licensed taxi, and discuss the fares ahead of time. When you leave the port terminal there should be plenty of taxis available, if you are unsure if it is a licensed taxi or not, ask a police officer.