The cheapest food that I know of, that is actually not completely junk, is spaghetti. I make the sauce myself, which makes it extremely cheap (tomato sauce + olive oil + some herbs) and the spaghetti themselves are cheap as well. Don't know the exact price, but it's hard to undercut.
You're a dog! Now I want spaghetti for dinner. I'm sure that the price I'll pay for all the ingredients needed will surpass yours. I'm now going to Walmart and will pay for the items separately. I'm sure it'll be over U$15.00, of which I'll take a pic of the receipt and post it here in about an hour. The only items I have on hand are salt, pepper, onions, oregano, and basil. I may or may not purchase grated Parmesan cheese.