In these large operations, when the hens pass their prime laying age, they are promptly evicted from the barn and a new batch of birds is brought in. Due to the economic absurdities of operating at this scale, often these birds are just killed. This is a great opportunity for someone with a backyard flock to get several bird at a low price or even free, and though they're past their peak laying age, these birds still have many eggs left.

Obvious disclaimer: Do Not start stalking chicken barn operators, and do not just show up at a poultry operation, there are biosecurity rules. But if you happen to meet one of these farmers and you casually mention in the conversation that you would be interested in a few hens when they age out of their operation, then you might just get some cheap or even free chickens.