Epcot:
Joy of Tea Stand (Kiosk near lake in China) has a meal deal which is great for Lunch or Dinner. Lucky Combo - combination of Pork Bun, Chicken Pocket, an Egg Roll, with your choice of a soft drink and an ice cream $9.98 This meal is yummy and comes with drink and dessert for under ten dollars.
Kringla Og Cafe (counter service in Norway) has a nice soup and sandwich combo for just under ten dollars. The soup is very yummy, filling, and comforting on a cool day. Outdoor covered seating.
If you want to eat indoors, Yakatori House has not only a beautiful Japanese garden to enjoy outdoors, but a small indoors eating area as well. The Japanese Curry dish is $8.50.
Magic Kingdom:
Columbia Harbor House has indoor seating, usually more quiet upstairs, and some of my favorite eats. My daughter and I can happily split the Lighthouse Sandwich and a Bowl of Chowder. The total for both is 12.78 before tax. If you get waters to drink it comes out less than $7 per person.
Casey's Corner has an all beef hot dog meal, with either fries or apple slaw for $6.59. Add in a box of Cracker Jack at $1.50 and your meal is only a little over 8 dollars.
Hollywood Studios:
Starring Rolls has outdoor seating, but they have a HUGE sandwich that is perfect for sharing. Their black forest ham sandwich, with chips or fruit is a little over $9 and the Chocolate Peanut Butter Cupcake is rather pricy at a penny less than $4, but it is amazing (frankly all their cupcakes are astonishing) and if you are splitting this meal the cost per person is still less than $7 each including tax.
Studio Catering Company has a Greek Salad for $6.50 with Kalamata Olives and Feta Cheese. It was very good.
Edited to add: My son just corrected me and informed me that Casey's no longer had an all beef hot dog, they are now a beef/chicken dog served on the new Disney Bun. While we eat exclusively whole grains at home, the new buns are astonishingly dry and fragile. They fell apart on our last trip and tasted like eating napkins. They are a blight on the good name of whole grain everywhere. So, I sadly remove Casey's from our recommended cheap eats list. My son recommends heading to Main Street Bakery where a tasty Ham Egg and Cheese Croissant and Cinnamon Bun as big as your head will set you back a bit less than $10.