I do not currently have chickens, nor have I ever made homemade chicken food. But I've been raw feeding my carnivores for over a decade, probably coming up onto two now. I've also made rodent food and parrot food. I've gotten the 'you can't do it', 'you don't know what to do', 'you'll harm/kill your animals' and a lot more. I will say that feeding carnivores is a lot more straight forward than feeding omnivores or herbivores. I manage to feed myself without nutritional deficiencies just fine.
It is easier to just buy commercial feed, and sometimes cheaper. If you are set on homemade food do a lot of research, learn what your birds need and in what percentage. Learn about the nutritional makeup of different foods. Not all foods are equal even if the percent of a given nutrient is the same. Remember that chickens are not vegetarians, they need complete protein. And while you can get away with the right mix of plants for it IMO it is not the same. Add some animal and/or insect protein into your mix. Depending on the number of birds you have this could be pretty easy or take a lot more work. Ex, I have omnivore reptiles so I raise my own feeder insects for them. It is super simple, but if I had to upscale it, it could end up taking up a lot of time and space.
People tend to over complicate feeding and nutrition. It is doable, but takes some research. I'm still reading up on nutrition and learning new things. Sometimes I try something that doesn't work, so I change it. Sometimes I learn that something isn't necessary. I do have a theory too about feeding animals. I think sticking more closely to the recommended percentages is more important for high production breeds of animals. Their bodies are on the verge of some key nutrients due to using them them in making whatever it is. I don't know if this is true, but it makes sense to me. Maybe on a homemade diet your birds will produce a few less eggs or grow a little more slowly. Maybe not.
I'm not sure where I am going with all this, I just wanted to jump in seeing all the negatives I see about making homemade diets. It is possible, it's a matter of if it is something you are willing to put the time and money in to.

Very well said.
I just think most people won't take the time to do the research. As noted, it isn't as simple as 10 lbs. of this, 3 lbs. of that and 1 lb of the other. Not only would a grain/legume diet be deficient in some amino acids, Vitamin, mineral, fat and fiber content needs to be specific for growth, production, and immunity in poultry and normally need to be added as supplements.
One of the main things that impacts cost for the home producer is the economy of scale. The home producer would be buying vitamins and minerals by the pound while feed companies are buying by the ton. We would buy grains and legumes by the 50# bag while feed mills are buying by the trainload.
In addition, buying vitamin supplements to add to a feed mix lose potency quickly.
Small feed mills I know have ceased making their own feed because the supplements go bad before they can be used. If a feed mill can't make the feed in a timely manner, I doubt an individual without a proper hammer mill, mixer and an assay lab could do any better for less.
As you said, feeding raw to carnivores is a much simpler process. A friend of mine has been feeding raw to carnivores for decades as well.
I worked doing maintenance, feeding and caring for a scarlet and great green macaw breeding program. The biologists in charge of the program would have much preferred a pelleted feed but we had to scrape together things that would provide the correct nutrition. It was a daunting and time consuming process to feed 400 of these avian giants. We would buy fruits, vegetable, and root crops cheaply on the brink of spoilage at the market. Supplemented with gallo pinto (cooked rice, beans) and a vitamin and mineral blend meant over 25 man hours each day just to prepare the food.
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On the OP's list was whole black oil sunflower seed. While it has a fairly good amino acid profile, it is way too high in fiber. Chickens need about 5% fiber. BOSS contains over 20% fiber. The 18% protein and 30% fat are absorbed by and used to process the fiber. Whole oats is also mentioned. They are to be avoided since they are over 10% fiber.
The OP has 25 chickens. I don't think that is enough to use the Nutri balancer before the vitamins are lost in it. Nutri balancer comes in 60# bags that is to be mixed with a ton of grains/legumes. That's another $75 added to the price of the grains and any sources of protein. I don't see 25 chickens eating a ton of grain within 6 months.