Hi Lisa,
I love to look at the menus on the dining pages at
www.allears.net they are updated regularly and list the prices.
There are lots of quick service restaurants throughout Walt Disney World, all with varying prices, so I will give you some approximate prices for food at Cosmic Rays in the Magic Kingdom. (please note prices are approximate and subject to change)
1/4 pound cheeseburger and fries - $6
Grilled Chicken sandwich and fries - $7.20
Chicken caesar salad - $7.20
Vegetarian wrap - $6.80
Childs chicken nuggets meal which includes 2 sides and a drink - $4.50
Brownie - $2.40
Carrot cake - $3.60
Soda - $2.10 or $2.40
Bottled water - $1.25 or $2
If you all have a meal you are looking at approximately $28 for a family of 4 to dine. We have always found the portions at Disney to be huge though and have always shared 2 adult meals between the 4 of us (children are 10 & 12) Depending on how hungry your family is you may want to consider that as it will really decrease costs. Also all restaurants will give you free iced water if you ask, this also saves you drinking too much soda!
Hope that helps and have a great trip,
Jo