Vegetarian lternatives to meat / eggs:
Tempeh, tofu, dried peas and beans. TVP is a little hard to find nowadays, but it’s cheap. The fashionable meat analogues (Beyond Meat, Impossible Burger, etc.) are budget busters, and overprocessed.

Cheap alternative to rice:
Grits. If you make them really thick, you can use them as a bed for beans (especially black beans). You can add lots of flavorings and ingredients (garlic, jalapeno peppers, imitation bacon bits / tempeh….) to compensate for their blandness.