@jnl
My best tips for cheap cooking are this: learn how to cook potatoes, rice, and beans. Potatoes will always be dirt cheap, and rice is an excellent calorie-dense food.

Between potatoes, rice, beans, and butter, you will never be hungry, and it will take a very long time to develop nutritional deficiencies if you have to live on those exclusively.

Learn a bunch of different kinds of meals that use those ingredients.