As one who is raising her own food on zero income right now, this is very real to me. My husband and I both lost our jobs a year ago and have not been able to find work since. We've run through all our savings, and only get any money by selling things we own that we don't need, doing the occasional odd job, or donations from our religious group for my husband's teaching. We just plain can't afford feed, but when you are Jewish and live in a town with a Jewish population of less than 10--and only four of them practicing as far as I am aware-- kosher meat and dairy products are not available at all in grocery stores. So we have to raise our own.
We've got five goats--two milking does, our stud, one that we're getting ready to butcher, and another young doe we will start milking this year. We eat the males born from our girls and sell the females as milk goats. They don't bring any money around here though, it probably costs more to produce them than we get for them. We also have right now three chickens, but are saving up to increase to a flock of about 25, for eggs and meat for our family and some friends.
We buy hay for the goats because even though we have 7 acres, it is desert and they would eat everything on it in a few weeks if they were let loose. We can't buy the top of the line hay, we have to get whatever is the cheapest and sometimes pick through it to get rid of mold spots. I also allow them to graze about half an hour at a time a few times a week, under supervision. If it came down to not being able to get cheap hay, we are backed up to miles of open land where I could take them out all day to graze (under management so they don't destroy anything!). We are able to get leftover grain mash from a local brewery at $15 for about 300 pounds of it, which we feed to the chickens. The goats nibble at it too, but don't eat much. The chickens get all the food scraps from the kitchen--vegetables, fruit, meat, eggs, fish, dairy...whatever we have left over. I feed them egg shells for calcium instead of having to buy oyster shell, and they get their grit by picking up gravel off the ground. They also get some supervised free-range time. Protein here won't be a problem in the summer with so many bugs and lizards running around. In the winter, we could shoot rabbits to feed to them, I suppose. We shoot them anyway and throw them out for the coyotes, since we have too many rabbits around here. I'm also looking for a store or restaurant that would collect some food scraps for us to pick up, but if we have another serious depression, that would probably not be an option anymore. Since I have the means of gardening, I suppose I can also grow foods for the chickens.
I expect things to get a lot harder than they are now, so I am purposefully going to crossbreed chickens that are good for eggs/eating but good at feeding themselves and surviving on free range where there are lots of predators. I'm going to mix Cornish, several egg laying breeds, and some game breeds together and hopefully get a decent dual-purpose bird that's tough enough to stand up to predators and will raise its own young. If it comes down to it, I will just set them all loose to fend for themselves and then we can still eat them and collect their eggs.
"Back in the day" many farmers never bought feed for chickens. The chickens fed themselves, and maybe got some scratch just to keep them tame and make them stay around. That's how I raised them as a kid, and got more eggs than I could handle--most of my hens laid daily. Chickens in less developed countries live very well without layer pellets.