How much feed, scratch and oyster shell for 100 chickens per month. (we get lots of snow in winter). This would be for egg layers or multipurpose birds.
They don't need scratch so save your money on that. Calcium is ground into Layer formulas, but if you want to supplement a bit, that's fine. The amount would be minimal. Your real expense is the good quality feed. Those birds will eat 4 ounces each, per day. In the coldest part of winter, they'll even eat 5 or 5.5 ounces to help with heat generation. But, for the sake of planning, 4 ounces, or a pound of feed for each 4 birds, or 25 pounds a day. You'll likely be buying in bulk from a local feed mill. Hope you have tight feed storage bins. You'll likely buy feed by the ton. Current best prices around here is $20-$22 per hundred. Hope that helps.