I have been to Disney every year at leaset once a year for the last 25 years and have eaten at some great places and have some good ideas for you.
On Saturday (MK):
Eat lunch at Cosmic Ray's Starlight Cafe. Its a big restaurant over by Space Mountain, sort of in the center of that area. It is round and has several choices, its almost food court like in that you have several options, one side has burgers/hot dogs, one side has salads and soups, one side has I think more hot (substantial sandwhiches) and things such as chicken strips, etc. and each side has kid's choices, which if you aren't that hungry, make a good option for adults. I find that even though you are very busy on the go-the heat and hustle/bustle of the day sort of take away my apetite. I like this place because it offers something for everyone and is very reasonably priced. If you sit down in the lower part of the restaurant, there is a free animatronics show. Also-there are large topping bars to fix up your sandwhiches with things like lettuce, tomatos, onions, pickles, mayo, mustard, etc. Tip: Do not pay the extra price for the cheese burger, as you can order the burger plain and use the chese sause on the bar.
For dinner, I would recomend either the Harbor House near Liberty Square. They have chicken strips and fried fish baskets. Or there is a restauant over top of teh Small World that is good too-its basic burgers and sandwhiches. (Unfortunately I don't remember the name and all the restaurants are not listed on teh web site).
Sunday: MGM
The Backlot Express-which is near the Star Wars Ride. Its a simple burgers/chicken/sandwhiches, and has a topping bar similar to the Starlight Cafe (mentioned above).
ABC COmmissary-huge foodcourt with lots of choices.
All of these choices are indoor-counter service places that are reasonably priced. To keep cost down, avoid character dining and places with table/waiter service. The food is just as good at the counter service places.
If you are hopping and can hop over to Epcot, there are lots of international counter choices. Try the Food Fair/Food Pavillion (used to be a Kraft sponsored place, may be Hershey or some other sponsor now) but anyways, its a beautiful big open structured building that is full of tons of options at many different counters in one big building. Its in the future world part.
If you want something a little nicer, but reasonable-try eating at San Angel Inn, in Mexio in Epcot.
Let me know if you have more questions.