In places I've lived recently, canned tuna isn't the cheapest source, though it's cheap-ish. Canned chicken is cheaper in most of the USA. Even fresh or frozen

In places I've lived recently, canned tuna isn't the cheapest source, though it's cheap-ish. Canned chicken is cheaper in most of the USA. Even fresh or frozen meats can be cheaper, e.g. chicken in the USA, or pork in Denmark. As well as lower-end sausages and other processed meats. Plus, nearly all vegetable sources of protein, like beans or lentils, are cheaper than those. I would also not suggest canned tuna as a staple protein, because of its high mercury levels. It's okay to eat occasionally, but eating ~10 cans/week as your main source of protein isn't a good idea. The safe consumption quantity for a typical adult is in the range of 2-3 cans per week of chunk-light, or 1 can/week of albacore.