Cheapest Lunch at Walt Disney World:
We head to Beaches and Cream at the Beach Club Resort, we grab the boat from Hollywood Studios and then we order the Kitchen Sink. At $23.99 this thing boasts eight huge scoops of ice cream, all the toppings they offer: Marshmallow, Strawberry, Pineapple, Peanut Butter, Hot Fudge, Butterscotch, & Chocolate Syrup topped with nuts and an entire can of whipped cream. Keep in mind this is a sit down restaurant with a server, so you need to plan a tip in the cost of this meal.
They usually make a big hoopla when they bring it out. My kids are normally fed a diet of whole grains, steamed vegetables and fruit for dessert, so to have this as a lunch just flips their collective lids.
We all leave stuffed and have really wonderful memories of this lunch.
Also at Hollywood Studios is Starring Rolls Cafe. The sandwiches are HUGE and easily split between two people. They come with either fruit or chips for $9.19. Add in a few waters to drink and you have a relatively healthy meal that will not break the bank. As a counter service meal this will not include a tip, but it only has limited outdoor seating, so this is not a great place to eat in bad weather. It is also snuggled up next to a smoking area. So, we usually get our meals and eat them elsewhere. The cupcakes here are beyond delicious and HUGE. They need to be split at least two ways, maybe three. At $3.59 they are more expensive than I would pay at home, but they are incredible in taste and so large as to make them a more reasonable price if you consider it is at least two servings.
As for another sit down restaurant, you may want to consider dining at the Plaza in the Magic Kingdom. They have nice sized sandwiches for 10-12 dollars which come with broccoli slaw or house made chips or fries. Their kids meals are only a few dollars less expensive than the adult entree, but we have had them split an adult meal between kids before without difficulty.
The Animal Kingdom offers Yak and Yeti, where you can pick up a couple main meals such as sweet and sour chicken $9.99, served with white rice and then top it off with a few pork egg rolls, $3.99 for two.
In Epcot, to eat inexpensively, I would get a couple Vegetarian Platters from the Tangerine Cafe. These are nice sized platters and filled with yummy treats. My kids all enjoy eating here. At only $9.99 you get a large oval plate filled with food. Then you can grab a dessert over at Norway. The school bread is only $1.99 and very yummy.
Also at Epcot is the Joy of Tea Stand in China. This place boasts a wonderful value for Disney. You can get the Lucky Combo - combination of Pork Bun, Chicken Pocket, an Egg Roll, with your choice of a soft drink and an ice cream $9.98
These have always been served hot quite tasty. Their ice cream flavors sound a bit wild, strawberry red bean or ginger caramel, but we found them to be very subtle. This place is great, but you will be eating wherever you can find space as it is a kisok.
I hope you find what fits your pocket book and family taste buds.