I second the recommendation of soup. Soups are tasty and can be very inexpensive to make. I eat a lot of split pea and lentil veggie soup. Also, bean chili has a ton of protein and although most chilis are very spicy you can spice it to taste.
I lived like a pauper in college, but instead of using packaged processed food like most I stretched healthy food. Tip: Try to find a shop that sells vegetables more cheaply than the grocery store. The vegetables will probably be fresher too.
Let’s see…what else. Bananas and oatmeal is a fantastic, cheap, filling and healthy breakfast. Also, eggs are a fantastic cheap source of protein and nutrients. But generally, rice and beans, beans and rice, and more rice and beans.
It helps a lot to invest in good, fresh spices.