I make a lot of meals for my roommate and myself with 2 cans of tuna ($.69-.89 a piece) and a package of 'parmesan couscous' ($2.49). The couscous part can be broken dwn even further if you just buy a big thing of couscous without the flavoring and make your own.

Total: $3.50 for two people. You could probably feed three with it, the servings are huge.