For our family there's just no way the DDP is a money saver. I make a Costco run at the beginning of the trip & just pop a frozen entree into the oven most days. Add some bagged salad, milk and/or sodas (hey, it's vacation) & a pre-made dessert and the cost for a dinner for my entire family (mom, dad, g'ma, g'pa, 2 teenagers, and 4 younger kids) is still about $25.
Breakfast is usually cold cereal & milk. (Kids' choice, not mine. I always either make a smoothie or some oatmeal.) Total cost for whole group: about $10 per breakfast.
Lunch: sandwiches, (cold cuts, cheese, tomatoes, etc.) fruit, chips, veggie tray items, etc. Total cost for whole group: about $20 per lunch. (Cost is a little bit higher on lunches than you might expect because we always use paper plates for lunches so nobody has to do dishes.)
Snacks: fresh fruit, microwave popcorn, veggie tray items, ice cream bars, granola bars, etc. Cost is about $.50-.75 per person per day.
We typically do one or two character meals (usually breakfast or lunches because it's pointless to try to do a dinner if you have a tired, cranky toddler with you) with the whole group each trip and then DH and I will also go out to dinner a couple of times, leaving kids either with g'ma & g'pa, or with the Fairy Godmothers. For us, the cost of the Fairy Godmothers is less than the cost of taking the kids out to eat with us (!) and DH & I can enjoy a little bit of time away from it all.
Still, our family usually spends about $50 TOTAL per day on food (excluding those few meals out)--and that's purchasing a lot of "convenience" foods that require very little in the way of preparation. I believe the DDP is close to that per person. It looks to me like the more people you add, the more the numbers are in your favor for using that DVC kitchen!