Trails End buffet at Ft. Wilderness campground is pretty reasonable. Your 2yr should be free and the 4yr will pay the child's price. Pricing as per AllEars.net: Bfast: 11.99/7.99, Lunch 12.99/8.99, Dinner 17.99/9.99 There is a sing along campfire that starts near sundown, so if you had dinner you could go over for the campfire (Chip and Dale are there), stay for the Disney movie and call it a night. There is no charge for the campfire or movie, so a really nice night of family entertainment. Obviously you can do those two things even if you have dinner elsewhere. There are pony rides over there too, but I know your 2yr is too young, not sure about your 4yo. It rained the day we were headed over there, so I can't give you a review. Its on our list for next year.
Not sure where you are staying, but check the menu at your resort CS. We stayed at CBR and for $7.09 we got a breakfast platter that included: scrambled eggs, potatoes, slice of french toast, biscuit, bacon and sausage. We said no thanks to the meats and still didn't finish the platter. The three of you could get a great start to the day with that meal. For dinner ($7.99 to 9.49) you could get two sides plus things like salmon, chicken, pot roast, pork etc. Their kids meal are just $3.99.
If your kids will eat well first thing sharing the bfast platter, nibbling at the park and then a more substantial dinner might work well for your budget. Be sure to see if there are combo meals. I had selected a small pizza and the CM let me know it comes as a combo. I ate the salad and some pizza ends (thanks nephew) and my nephew ate all the pizza he wanted. We were both happy and got two meals out of one. My salad was very fresh and nicely packaged, I didn't even add dressing to it. Finally, get complimentary water for some of your beverages. In the heat you need it anyway and its a great way to save your budget.
I would also pack juice boxes in my checked luggage. You can then have them in the room and grab some each day for the park. Put them in a ziploc bag to be safe, but they'll pack really well.
My favorite Disney snack is the Mickey bar. Nephew liked the itzakadoozie popsicle and the apple slices with caramel dip(sometimes w/o the dip). I'm not sure if Mom would say the Dole Whip or popcorn, she double dipped on both! I must confess that I didn't meet a slice of carrot cake I didn't like (Main St. bakery HUGE or resort CS).
Here's wishing you and your little ones as much magic as you can stand at Disney World!