When I was broke-broke, I lived out of my friend's coffee shop's day old bagel bin. I'd get a dozen of those for two bucks, buy some cheap cheese and make a heartier version of grilled cheese by melting it over top of those in the oven. A head of iceberg lettuce lasted forever if you trimmed the brown parts off and potatoes were the best cheap food I knew thanks to my grandmother's stories about the Depression. Eggs, too. Cheap protein. A baked potato, even without butter or any other fixings, is like the most comforting thing to me.
There's a couple of things that I've learned to make from scratch that everybody thinks are genius things but they're very simple: Pasta and bread. They're both somewhat time-consuming, so I don't know if they'd work for super-busy families, but you can make them for company and they seem fancy even though they're not expensive. I buy lots and lots of flour, and for pasta all you need are eggs and oil, and for bread all you need is yeast. You don't need a fancy machine for pasta either, just a rolling pin and a pizza cutter or sharp knife.
The bread dough turns into cinnamon rolls in the morning, pizza on football afternoons, flatbread with whatever's left over in the fridge thrown onto it. It's a great way to throw a party for like $10.
What are your secrets for cooking cheap? John mentions a whole chicken, and I buy those when they go on sale, too, and use the carcass for stock. And a ham is the best thing for making something stretch forever. Meat is pricey but I find myself spending the most money on fruits and vegetables because it seems like those things go faster.
I swear to God, all I do in winter is eat and talk about food all the time.