Here are my picks:
Rancho Del Zocolo~
Get two of these and bring your own water, use your AP discount, and 2 can eat for under 20- and be stuffed.
Red Chile Enchilada Platter -- Four Cheese Enchiladas with Red Chile sauce. $9.49
Royal Street Veranda~
Creamy Clam Chowder - Served in a sourdough bread bowl $8.69
Steak Gumbo - Served in a sourdough bread bowl $8.69
Vegetarian Gumbo - Served in a sourdough bread bowl $8.69
Split one of these and you will be stuffed , you can eat the bowl!
Coca~Cola~Corner~
Kid's Hot Dog - Served with a fruit cup or Fruitabu Organic Fruit Snack, fun straw, and choice of small Low-fat milk, juice or small bottled water. $5.59
Chips and soda available upon request
Or you can do the Chimichanga or Turkeyleg route. The Turkey Legs are $7.50- o$8.00. I think the Chimichanga's are around $6.00.
The Turkey legs are huge! But then you will need a nap.
If you like coffee, get a cup at the Market house, save your receipt and get free coffee all day long. You dont need to save the cup just the receipt.
I would stay away from the Bengal BBQ. It is really good, but to get enough to fill you up, you might as well go eat at a restaurant. Good for a snack though but not if you are hungry hungry.
I am not a corndog on a stick kind of gal but I hear they are to die for.
You can go to allears.net to see all of the menus with prices.
My best idea is to bring your own water, and eat a big meal before you get to the park. Get there full or your food budget may go out the window.

Have a great time!