Our experience is this.

We went to Breezes Grand Negril at the end of November 2011 and after the smoke cleared, it cost us $3,565.00 for the two of us. The year before we spent 6 weeks (my wife spent 7). 2 weeks at Whitesands on the beach and the rest at Seastar Inn on the west end. Our overall cost for this trip was a bit under $7,000.00. 6 times as long (7 for my wife) for twice the price. This total includes all food, drinks, rooms, things to do, flights and transfers.

Having said that, I know you can get AI's cheaper than our experience but you definitly get a much better sense of the local vibe as it were, off AI in my opinion. Our best vacations have always been off AI. Off AI isn't for everyone but it is for us! I like feeling not obligated to eat or drink where I don't want to because of the price paid to be there.

Peace
Elvino