It would depend on the type of chicken (size).
I have had bantams who hardly eat anything, and I have medium sized large breeds who eat reasonably, but I also have some larger dual purpose who are hogs - and if it is within reach, they eat it.
The medium sized chickens lay good eggs - large to medium sized - the dual purpose lay huge eggs - large to extra large, and a lot of double yoke eggs, so it is a matter of what size eggs you want - the bantams laid small eggs (some of them were VERY small, since the chickens, themselves were so tiny).
With just the medium sized large breeds for egg layers, I was using maybe slightly over 150 pounds of feed per month. I had a flock of about 25 of them. I am down to a flock of 12 on the medium sized birds - they are a mix of various breeds. With the flock of 12, they eat (usually not cleaning it up) about 4 pounds of feed a day, and they freerange, but in this weather, there isn't much to be had freeranging. In the summer they eat a lot less than this.
In summer I save a lot of money on feed, because even though I put it out there for them, they are happy to eat bugs and grass and other various weeds and munchies they can get to.
so, if ya got through the rambling,
if you have 25 medium sized egg layers, you can probably get by with about 150 pounds of feed a month - if you supplement it with greens and other goodies.
I buy my feed in 50 pound bags, and mix my own with other grains and such. I pay probably (total of the mix) about 15 bucks per 100 pounds of feed. But then, I am not buying Purina or Dumor - those cost more than the feedstore mix I buy.
I am thinking of switching, however to a more expensive mix, since I am getting ducks and geese, and would like to feed them all the same stuff - which near me would be Flockraiser (purina brand) which sells for about 12 to 14 bucks for 50 pounds.
meri