Free ranging is the easiest way to save on feed. Mine will eat less than 1/2 their normal feed when they are out during the day. Giving them all your kitchen scraps, cleaning out the freezer and cupboards will help. Start a garden with vegetables you can supplement their diets with. I grow lots of extra winter squash. It will keep for months and you can cut one open every few days. If you have friends that homebrew, you can give them the spent grains. A compost pile can be a great source of food. They naturally attract larvae and worms. I've never done it but mealworms are cheap to raise. Don't try to replace their layer with these. It will cut into your egg production as the extras are often low protein, low calorie.
I stick with a locally milled 20% protein layer feed. I'm supporting my local farmers and mill, it's fresher, it's cheaper than a national brand, has a smaller carbon footprint and bottom line, I do not see a difference in consumption or production with it. In the winter months, I go through a 50# bag in 7-10 days with 25 chickens (mostly DP hens) and 7 guineas. In the summer than bag lasts over 2 weeks because of my garden and bugs.
