Buffets CAN be a good value if the entire party of 7 is going to eat enough to justify the cost. However, be aware that everyone age 3 and over is going to pay the going cost. You can't share the buffets and you can't purchase items of lesser value to save money - everyone is going to pay the same price whether they eat tons of food or two chicken nuggets. The current prices are rather high for the buffets, which lessens their value to any party that is not going to eat mass quantities and are not just interested in seeing characters (not all buffets are character meals, but all character meals are buffet or family style).
Pretty much any a la carte restaurant will allow parties to share food, so if you are going to split orders any of the restaurants that are not signatures will provide good value for that. If you are not going to split meals, avoid the signature (more upscale) restaurants entirely if you are looking to save money. If you have to be inside a park, try the Plaza restaurant in MK. It's really only a sandwich place, but priced less than the other restaurants there. I don't think 50s Prime Time at DHS is horribly expensive and the portions are large so sharing is a possibility. Epcot restaurants tend to charge more, I think. Possibly the best value there is Biergarten for lunch, and it is a buffet. Counter service is generally good there, so if you are looking to save money at Epcot that may be the way to go. The only non-buffet restaurant inside AK is Yak & Yeti. It is not inexpensive. There is a Rainforest Cafe just outside the gates; that isn't inexpensive either. These are not Disney-operated restaurants; not sure about their policies on sharing.
Some non-signature restaurants cost less than others. I'd look for restaurants in resorts if you can; some of them seem to charge a little less than in-park restaurants. Check the menus online to get a ballpark estimate of what restaurants charge.