Making your own black beans is cheaper but canned beans is quick and easy. There is a downside, however. A whole can of 3.5 servings has about 50 mg. These beans only have 15 mg of sodium per serving (1/2 cup). Black beans also provide a lot of fiber and you know we all need more fiber. Cost? Reasonable, particularly in bulk but still cheaper to make your own.
Remembering Mark Bittman's article in the NY Times — about $28 to feed a family of four at a major fast-food chain and $9 to feed a family of four with rice, beans, and vegetables.