What is the absolute cheapest things you can eat while still staying healthy?

So I don't care about food. I like good food, don't get me wrong, but I can pretty much eat anything as long as it doesn't taste bad. And during the work week, I mostly just want to fill my stomach. This is also partly just a thought experiment

So what I am looking for is foods that are inexpensive, healthy, and don't taste like shit. They don't have to be the most delicious things ever, just not taste like shit. I'm wondering if there is something like oatmeal, but containing all of the nutrients you need on daily basis.