We went in October and found a great deal. There is a hotel next to Atlantis (literally a 5 min walk if that). You book a room for the night. We paid$ 195. This gives you a room that includes 4 arm bands to Atlantis. This entitles you to everything at Atlantis. You can also have signing priveleges (sp?) at Atlantis for drinks, etc. We did the dig and water slides all day. It was also nice to go back to the hotel and shower. We had four in an interior cabin on Sovereign.
One tip....pay for your room with credit card and leave it open. You cannot buy any food, drinks, etc at Atlantis. You can only sign for them. Then you just settle up back at the hotel.
As far as a taxi. We just got one when we got into port. If I remember right it was $4 pp. We took Myself, husband, 11 and 8 yo daughters, brother, sister in law, 17 yo niece, and 5 yo nephew. All had a ball.
Oh, the name of the hotel is Comfort Suites - I think there are two so just make sure it is the one that tells you about the Atlantis priveleges.
Let me know if you have any questions! Michell