This is a pretty good one:
Get a soup-can sized can of refried beans. Whichever kind you can stomach the taste of. I prefer Goya. This can costs under a dollar at the drugstore by my house.
Half a can should be enough for one person. Put half a can in a pot. Add water by the tablespoonful and stir over low heat, adding more water until it is a thick soup. Thick is much better than thin.
Serve. There you have it, one meal for a dollar or less.
(You can also serve this with toast, or grilled cheese, or leftover taco shells, or cornbread, but the soup is pretty filling on its own.)