Nothing about Atlantis is cheap. Weve stayed there twice (anniversary present fom my parents, and reward for top sales by hubby). Its an impressive place though. You can tour the inside casino, shops for free but the Dig, pools, and slides all require a wristband. You can tour the grounds and Dig for about $25 pp, but the only way to use the pools, and slides is to be a paying guest fo Atlantis or Comfort Suites (and I guess now Best Western). The slides look like a lot of fun. Unfortuantely both times we went I was pregnant with both kids. Most of the restaurants are buffet style and it will run around $30 pp. A burger will run around $15. The food is so so, and the service is the same (it had improved on our second trip).
If you just want to go and see the place, its worth the tour. Personally I think a day room is a waste of time and money just to use the pools and slides since the place is so huge. The other thing, if you take the water taxi it doesnt drop you off at Atlantis (unless it does now) so be prepared to walk several blocks. And leave plenty of time to get back to the ship as traffic can be a mess in the afternoon.