I can do rice with canned veggies for about $2.25 and have enough to feed my entire family of 5 for two meals. I cook 3 cups rice and use 3 cans of vegetables (usually mixed veggies, green beans, and a can of beans for protein). Canned veggies are 50 cents a can at my local grocery (so $1.50 for the veggies) and I buy the rice in bulk so I figure about 75 cents for the 3 cups of rice. $1.25 to feed 5 people is pretty cheap!
Another really cheap meal my kids really like is ramen. I don't use the sauce powder (because it contains MSG and a bunch of other things), but I'll cook the noodles and add vegetables and beans to them. I can get ramen packets for 6/$1.00 here, and I usually cook 5 for my family of 5 (and have enough leftover for a lunch or two). That's another meal that can feed the whole gang for about $2.50 or so.
Kraft macaroni and cheese has recently changed their formulation so it's natural - no artificial colors or flavors. I can get that for around 50 cents a box (sometimes a bit cheaper) and 3 boxes are plenty to feed my family (each box is 2.5 servings, but we eat a bit more than that if it's the entire meal). I often add mixed veggies to that as well (and cut up hot dogs, but if you're vegetarian that would be a no-go). Total cost with the add-ins is about $3.00 or so.
Breakfast for dinner is another really cheap meal, if you eat eggs. I can get eggs for about 69 cents a dozen at Aldi, and it costs me about $2.00 to bake a loaf of bread. Add in some veggies (a bag of frozen spinach costs me about 1.00) and that meal is around $4 or so.