My family went to Atlantis last year.
It is the only place I have been that actually costs more then a Disney vacation. The food was outrageously expensive. We ate at a buffet most nights and for me, my wife, and our 5 year old daughter dinner was $155 each night. They had other cheaper buffets ($125) but they did not have the nightly chocolate waterfall.
You don't really save any money by leaving the resort. The cab fare and tolls to cross the bridge make up for the cheaper food you might find.
We stayed in the timeshare (Harborside) part of the hotel that we booked through expedia. We had a basic one bedroom. It was much smaller then a
DVC 1 bedroom. They also have deluxe 1 bedrooms that look to be about the same size as a DVC 1 bedroom. They have a shuttle that runs about every 10 minutes that takes you from Harborside over to the main resort. They also offer a grocery shuttle that gives you a few hours to shop.
We had an incredible time. The weather was perfect. The beach and pools were great. We spent our days going from pool to pool to beach and back to a pool.
You have to be 48" for all the water slides. At the time our daughter was 47" but a great swimmer. We got her some tall water shoes and most (but not all) of the life guards let her on the slides. Some would comment on her "nice" shoes but still let her go and others would make her take them off to measure.
I would go back in a heart beat. I just need to save for the trip.