Not sure if this will help but :
http://www.allearsnet.com/menu/menus.htm
These are menus with prices for all of the onsite restaurants.
Some of the counter service places are pretty reasonable. Remember, you can always share food. Also, the servings of fries and other sides are pretty big so ordering one or two for your whole group instead of one for each person is just fine.
Some examples :
Animal Kingdom
http://www.allearsnet.com/menu/menu_piz.htm Pizzafari
individual cheese pizza $5.49 + a drink $1.99 for a soda (or just fill up a water bottle and drink water)
http://www.allearsnet.com/menu/menu_tus.htm Tusker House
Kids Mac & Cheese w/applesauce and crackers- $3.99
Adults 1/2 Rotisserie Chicken served with garlic mashed potatoes and fresh seasonal vegetables $7.99
MGM
http://www.allearsnet.com/menu/men_coms.htm ABC Commissary
Child's Chicken Nuggets (with French fries and child's beverage) - $3.49
Adult's Fish and Chips - $6.79 - (battered fried fish served with thick cut fries)
Magic Kingdom
http://www.allearsnet.com/menu/men_chh.htm Columbia Harbour House
Fried Chicken Strips - Served with choice of either French Fries or Carrots $6.59
Kids Macaroni and Cheese - served with fresh grapes and cheddar crackers and child's beverage $3.99
http://www.allearsnet.com/menu/menu_pin.htm Pinochios Village Haus
Gideon's 1/4 Pound Cheeseburger (w/carrots or fries) $5.79
Child's Hot Dog with fries or carrots, mandarin oranges and child's beverage $3.99
Epcot
There's so many to list in Epcot...
http://www.allearsnet.com/menu/men_cant.htm Cantina de San Angel
Tacos al Carbon - flour tortillas filled with grilled chicken, onions and peppers, served with black refried beans and Mexican salsa $6.99
Plato del Nino - child size beef burrito, tortilla chips and a small soft drink $3.49
http://www.allearsnet.com/menu/menu_eu.htm Electric Umbrella Breakfast
Cheese Omelet Meal - cheese omelet served with hash browns, a mini biscuit and choice of sausage or bacon $5.29
Cereal (Frosted Flakes, Rice Krispies, Raisin Bran, or Special K) with whole or lowfat milk $1.99
http://www.allearsnet.com/menu/men_li.htm Liberty Inn
#2 Turkey Sandwich -smoked turkey breast, muenster cheese, spring lettuce mix and chipotle mayonnaise on an everything bagel, served with salad $6.59
Childs choice of hot dog or chicken nuggets served with fries, applesauce, and a child-sized Coca Cola $3.99
etc...
So there are options for cheap meals under $10. They are esp. cheap if you bring a water bottle from home (Brita ones work great) and continue to fill it up. I find water to be the best beverage anyway, on a hot day in the parks.