I have a cockerel flock that I keep as pets, I have raised them from day old. I too, try to keep the food bill down, because they do eat lot, lol.
It depends on where you are. Here, we can get on-expiry bread for free when we spend enough in a local store, we can also got okara for free from a local bean curd/soy milk shop. We just boil the okara for 5-10 minutes and give it to our cockerels, together with chick starter, chicken scratch, about to expire rice that we purchase from a discount store that sells about to expire food.
If you have a large compost pile, your chicken maybe able to supplement their diet with worms & crickets etc in the compost pile. If you chickens free range, they will also eat a lot of grass willingly.
On our hobby farm, we grow sweet potatoes, sorgham, corn, and sunflowers, so our chooks also get those crops. But like I said, our cockerels do eat a lot, and as a hobby farm, those crops are hardly enough for them.