Rule of thumb for Cornish cross is that they will eat 17 pounds up until 8 weeks, when they can be butchered. You will have to do the math yourself.
Cost per chick varies by how many you buy and who you buy them from.
Processing costs depends upon whether you do them yourself or pay to have them done.
At 8 weeks on the dot, mine had finished off 17 pounds of 20% turkey feed, but I'd put 2 bags of meat bird crumbles through them when I first got them, so that was another 2 pounds of feed per bird. Then, I am running them on for another week and butchering at 9 weeks, so a couple more pounds of feed per bird. I'm looking at 21 pounds of feed per bird from start to finish.
It's cold here and I suspect that the birds were using some of that feed to keep warm instead of to grow. They look good, though: nice and big and fat.