Anything with rice can be crazy cheap and still good. Grab a bag of red beans and rice and add a sausage to it, you'll easily feed everyone for about $5.
How about Chinese? Here's the basic equation, meat + garlic + ginger + soy sauce + vegetable (like broccoli or mushrooms) + MSG = delicious. (Yes, you do need the MSG. Yes, it's available at your grocery store - called "accent." Yes, it's cheap and no, it doesn't give ANYONE a headache. It's just how to get that professional, traditional Chinese flavor.) Season with MSG just like you would with salt. Once it's just about done add a tablespoon of cornstarch mixed with a tablespoon of warm water to thicken it up. Stir and bring to a simmer and serve immediately. Again, you can easily feed the whole gang for about $5.
How about Caribbean? Grab a box of Caribbean rice and some chicken breasts. Cut up the chicken, brown it and throw it in with the rice while it cooks. Another $5 meal.
How about stuffed potatoes? Grab everyone a potato and two cans of broccoli cheese soup. Bake the potatoes, don't forget to put a little oil and salt on the skin to crisp them up and make the skin delicious (it's the healthiest part after all!) and warm up the soup, add little to no milk depending on how thick you'd like it as a topping. Cut open the baked potatoes, add butter and or sour cream and or cheese and ladle in some soup. It's surprisingly good and crazy easy. Yet again, we're at about five bucks.
Frozen pizzas are cheap too, that can fill a day. Don't forget standbys like egg salad and tuna salad sandwiches. Breakfast for dinner is cheap and fun, omelets, pancakes, waffles.
Compare those to the salad someone suggested. Unless you're just serving iceberg, salads will run you at least $10 - $12. What's a salad without onions ($1), decent dressing($2.50), mushrooms($2), cheese($2), cucumbers($1.50) (add the lettuce and that gets me about $10.50) etc. And then, once you're done, everyone will still be hungry, yay!