Tuna with saltines or rice or in sandwiches is pretty affordable, too. That was my good go-to. Then of course there were things like toast with butter and garlic powder. Maruchan ramen, naturally (none of that Top Ramen nonsense). Oh, and french fries! A potato is cheap.
I try to limit my tuna to a couple times a week. I already bioaccumulate enough plastic and PFAs, don't need to add too much organic mercury to the pile. But agree on the maruchan.