Hi Vivanco- I answered booking tours on your own in your other post, but since this is a direct question I will help here also.
Yes you can just get yourself to Atlantis and pay to use the resort (day pass) I have NOT done this as its been forever since we have been to Nassau. But if you use the search feature of the forum you will find many posts on Atlantis. Someone had said in the past that there is a hotel across the street from Atlantis that had a use agreement with the resort and if you book a hotel room there you saved money on the day pass but that is old information.
Use a land taxi (the water taxi gets over loaded and in many peoples opinions are not safe). You can google on the Atlantis resort, go to their website and get current pricing. Then you can determine how much you would save doing it on your own. If it was one or two people it might not be much but on 6 people (or is it 7?) it adds up quickly (keep in mind you will probably need two taxis) Come back here for help there are several members that have recently been to Atlantis.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007