It really depends on what AI your staying at and it's location if going AI or not is less/more expensive. It also depends on the persons needs and wants. We usually go AI not so much because it's less expensive (in many cases it was), but for the sheer convenience.

Some people, including myself, don't want to buy groceries and cook on vacation. We do that at home. Vacation is getting someone to do that for you. Personally, I don't want to eat boxed cereal for breakfast or have sandwiches for lunch when I am on vacation, and from the comments of the OP, they don't either.

The OP has already chosen the Barcelo and has posted a new thread on the Mexico board.

Take a Caribbean cruise. It would be a lot cheaper than $3500 for 4. You can go to the beach on several islands, be fed and entertained for way less than $3500.

Gran Puerto Real is the best. It's AI and just beautiful.