Yeah only cheap if you don't include your time. And the cost of land. But as a Florida food gardener - OKRA is like nothing else. It grows even in the summer here, is beautiful, the flowers are lovely and my whole family loves it. If you grow it, you can pick them when younger, and the few you inevitably miss, save for seeds. Nutritious and delicious, and in hot climates, cheap.
Beans are the obvious answer to the OP's puzzle though. Beans and rice, build up your spice cabinet, endless variety and so delicious, cheap, and healthy.