The basic DDP (1 CS, 1 TS and 1 snack per day per person) costs $40 per adult per night, and I believe $11 per child ages 3-9 per night. Everyone on your ressie must also be on the DDP. Children under age 3 are not on the plan but eat free at all you can eat meals, and are also allowed to share with an adult at an a la carte restaurant.
I think the deluxe plan is around $72 per adult/night and $22 per child ages 3-9 per night. It includes 3 meals (any combo of CS/TS you want, or all TS if you like) and 2 snacks per day/person.
The CS plan I am not totally sure about but I believe it is $26/adult/night and not sure the children's price. I am guessing here on this one though. I do know it includes 2 CS meals, 2 snacks per day, and a refillable resort mug per person. We did not look very much into this one since we like to have 1 TS dinner every night on our vacation, and the occasional TS character breakfast too. Deluxe is too much for us, but the regular plan fits our needs most.
You can add the DDP 48 hours or more before your arrival. You pay for it when you check in.