My neighbor raises CX every year, and butchers at 8 or 10 weeks, food is kept in front of them at all times, and she says they eat roughly 1 1/2 to 2lbs each per day, so if I figured it right that's almost 500 lbs of feed or 10 bags at 15.00 a bag that's $150.00.
Now so far my dual purpose chicks are 19 weeks and getting butchered tomorrow, if mother nature co-operates. anyway I have gone through maybe a pound per day, so that's figures out to be, around 450lbs or 9 50 lb bags of feed over that 4 month period. and I didn't feed anything but unmediated Nature wise feed and greens and treats of course, they do have a run but it isn't exactly free range. so 9 bags @ 15.00 a bag $135.00
The 1 difference is my chickens are larger in body size, but not as meaty as the CX ,
So that's as close as I can give you an idea, it will depend on what your feed costs are and when you butcher. But remember chickens are lovable creatures and by the time almost 4 months rolls around, they may not be so easy to butcher. You may get attached