I like the Chili idea, I would be sure to add lean ground beef to that though. Other things you can think about are eggs. They are very cheap and eggwhites are an excellent source of protein. You can make baked egg dishes that have veggies in them (sort of like a fritata) and have that all week to eat and it is relativly in expensive. Oats are great and plain ol'quaker oats are very inexpensive.
One thing to remember is that carbs like beans and rice are not complete proteins. A protein is what our body uses to obtain all 9 essential amino acids to repair our skeletal muscle. Grains like beans and rice do not contain all amino acids needed in an of themselves BUT if you were to pair beans and rice together you would obtain an complete protein. Beans have certain amino acids, and rice has the others making a complete protein.