Never mind that dried beans are cheap as hell, easy to prepare, and taste pretty good. I mean come on... put them in the pot to soak overnight, drain them and replace the water, then boil for an hour. There is very, very little effort required there. If you want to add to that a bit, buy some flour, use one day a week to bake a loaf of bread (simple white bread is super easy), then make yourself beans on toast. Combine with some milk, fresh greens from your garden, and a single piece of fruit a day and you have a boring but extremely cheap diet.