One 6 ounce can of tuna packed in water has roughly 40 grams of protein and only about 200 calories. Add that to the fact that one can costs under a dollar and you've got a great and affordable source of protein.
My perfect paleo tuna lunch is super cheap, easy to prep and ready in a jiffy. Just slice up some cucumbers, open and drain that tuna, mix in olive oil and lemon juice to taste and plop that mixture on your cucumbers. Other variations, include mixing the tuna with fresh salsa or chimichurri and topping it with a slice of pickled jalapeño.
So when you're short on cash, ignore those drive thru dollar menus and just look for a can of tuna.