Beans are super! They are high in fiber, they're a great source of protein, they're inexpensive, yet they're very filling--a great part of the diet. A family of four, for example, could have a pound package--maybe use just half the package--and so that would be just a very few cents worth of beans, but that would be enough, cooked up, probably for the whole family to enjoy, and to make a center-of-the-plate entree, or a soup.
You can mix them with a small amount of animal protein, and stretch that protein, which may be higher in price, in addition to the beans, and have a very versatile dish, that's also going to be nutritious, because it has two kinds of protein, very high fiber, from the beans, and very inexpensive because you've extended that more-expensive protein, with the less-expensive beans.
Another reason that beans are so economical is because we can keep them for such a long time, and their quality is going to stay just as good. They'll last on your kitchen shelf for six months, easily, and long than that, if need be, without an appreciable decrease in quality.
So they're always good to have on hand, in case you have more "month" left at the end of your paycheck, than you anticipated. Maybe it's a good time to look in the cupboard and see what's there, and you might be pleasantly surprised to find a variety of beans on hand, that can make a wide variety of dishes, and keep your meals coming, even when your budget may be a little bit short.