My favorite menu for quick, easy and as cheap as I wish to make it is:

Spaghetti with Meat Sauce
Tossed Salad with assorted dressings
French or Italian bread
Dessert (usually Yogurt Pie or Pound Cake)

I use this menu at church frequently and it is always well received. What I like is that most of it can be made in advance. I put the meat sauce in a crockpot (I use ground beef, onions, garlic, Classico tomato & basil sauce, Italian seasoning, salt and pepper), buy prepackaged tossed salad and add a fresh head of lettuce. (Sometimes, depending on what's available, I will add additional vegetables to the salad.) I may or may not toast the bread and sprinkle with garlic salt, depending on my energy level and time available. The dessert is made ahead or while the meat browns. Anyway, I can make this for about 50 people in about 2 hours straight prep time and the cost is usually under $100.

Hope this helps.