Wishful thinking. You could get it down that low but you would need an amazing compost system and bug/worm bins.
AGREE.
I have acres of pasture in a VERY forgiving climate - a number of things are already in seed. My ducks eat roughly twice what a chicken does, so I have "64 poultry units" at the moment (my flock is in my sig, below). They have complete accesss to the pasture at all times. The "thumb rules" would anticipate that they need 16# per day to maintain top condition. I am currently feeding 11-12, and considering moving down to 10#/day. That's a considerable savings, don't get me wrong, but its highly seasonally variable.
Even if I can get it down to 10#/day for my flock, that's still 4.5# per bird per month or about 90#/month for a flock of 20.
I am NOT claiming you can't do better than I - to the contrary, I hope that it can be done or I can't improve upon my own efforts - but I am saying that's a very ambitious target even with free ranging...