Can you give us a general idea where you live so we can toss out some specific ideas?
Do you live in an area where you can plant some winter crops for them (green manure type)? Do you free range or can they be free ranged some of the time if you are home to reduce the food bill, assuming you have a quality area for them to forage? Can you raise the feeder so that the chickens can't spill the food?
Chickens don't need treats; want them yes, but need them, no. I think that BOSS is pretty expensive for 40 birds unless you are feeding just a tiny amount. My chickens don't get them and they are doing just fine and I make a salary where I could afford them if I wanted! Ditto with scratch. You could grow some sprouts for your chickens even if you can't grow anything outside and that would be a fine treat!
Can you glean or forage to supplement their diet and for treats? My girls love dandelions. Since I can't let them free range during the week due to my work schedule, I dig up dandelions for them. I also pull up kale, cabbage, and collard greeen plants from the almost-put-to-bed garden, give them pumpkins that others were throwing out (got 3 just today!), and throw a bucket of compost or leaves into their run for them to dig through during the day. Ask your local store if you can take leftover veggies for your chickens, maybe the trimmed outside scraps.
Feed your chickens the best that you can afford. And I agree - buy in bulk! I buy things like grit in 50 pound bags for less than $10. If you have to feed a lower cost food for a while, I'm sure they will forgive you.
I was at local organic agricultural specialty store the other day and found a pallet of things ranging from 10%-50% off regular price! Check with feed stores; they may have a broken bag of chicken food, cat/dog food (that can be fed in small amounts to the chickens) or something else you use for a reduced price, allowing you to spend more on the chicken food.
Is there another place in your life that can be cut or trimmed so you don't feel crimped in the chicken budget?
Is there a buying co-op in your area to help reduce your food and their food costs? In the western half of the US, you can use Azure Standard (
www.azurestandard.com). They have both organic Rogue pellets and starter for less than $22/50 pounds or organic Magill Ranch for about $28 - no non-organic foods available. They have tons of foods for you and if you buy your own foods in bulk, it might take the pressure off the chicken costs.
Can you use (free) leaves in the run and coop to reduce costs instead of straw or shavings? I got 10 burlap bags (which were also free from a local coffee roasting house) full of leaves from an elderly lady the other day. And coffee chaff (not grounds) works in the coop if you have a roasting house. They are free for the asking!
Craigslist!! I was first in line for some spent grains used in making beer. I got these before I had chickens but I could have fed these as the couple was literally pulling out the grains from the malt before my eyes. They were obviously not moldy. Check with local brewing establishments for spent grains. You may very well find lots of other edibles on Craiglist as well.
If you don't already, I'd suggest adding apple cider vinegar with the mother to the water. It may give your chickens an extra boost to keep them healthy. Just a small amount is necessary.
Good luck to you. I know it's tough out there.