If you have a huge property you could probably let them free range their entire lives free at no cost?  Even still, not sure if it's sustainable..... sooner or later the grass will be empty, field free of bugs, then what else is their to eat but each other's feathers?  I don't know, buying feed and supplementing them with kitchen scraps and free range time will dramatically cut back on the cost of chicken raising though.  That's what I've been doing after realizing they are actually little pigs and will go through bags of feed like it was nothing.  Also, what I've been doing is actually only feed them during a specific time of the day and not let them have an all-you-can-eat buffet style set up for them where I overfill the feeders to the brim and let them gorge whenever they want..... I sometimes feel like as chicken owners we sometimes feed them way too much by giving them free-will to eat whenever they want.