I figure my feed costs on the total grow out period using 14.5# per broiler. So I multiply that by the amount of birds I have ordered and only buy that much feed before processing day. I have seen some people say 9 weeks will take 13.3# feed per broiler, but I don't know if they are restricting feed or not. Both of those figures (mine and the one I saw recently) were based on dry feed, not fermented. I will say that it's more than 8-9 weeks that the 14.5# lasts my broilers, but I can't remember exactly how much longer.
I have read that laying chicks (who consume less feed than the broilers, all things being equal) will eat only 1/2 the amount of the same feed when it is fermented. I would imagine you'd see a similar tradeoff with the broilers. If I were you, I'd budget for buying up to 1450# feed for your flock (max), but only buy the feed weekly and track their consumption should you ferment - and share your results with us, too. If the tradeoff is the same, you might get away with only buying 800# of feed or so! And wouldn't we all love that? I may try it this year as well, but I have a lot going on at the moment chickens and otherwise.
I raise about 25 per 8'x8' chicken tractor, especially towards the end. There is a period where they're all in one or two pens right out of the brooder, but you will need the equivalent of four 8'x8' portable pens for 100 mature birds, and you'll still need to move them almost twice per day when they get close to market weight. So make them easy to move!!
I second, third, fourth, etc., the tips above about bringing the food out a few times a day, positioning of feeders & waterers, and pasturing them as soon as & as much as possible. Even bringing garden bugs and clumps of grass with the dirt and roots and all into the indoor brooding setting right away (provide chick grit) give these birds the idea that bugs and grass are food & fun.
OR free range them...
But if you free range make sure you give them lots of areas to hide.
I keep them in the tractor until 9 am or so and back in by 7pm... Stay away from the shoulders of the day predators love CXs...