I’m pretty sure they are eating it all because there is never more than a few crumbs on the ground from messy eaters, and I’ve watched them eat the feed. They just gobble it up with their mouths. The feeder also has high walls so they can’t scratch it out. I’m not sure if you can see from the pictures. I know I do have mice, but I haven’t seen a way for them to get in. I built the hutch pretty tight. I will start locking the feeder up at night and see if that helps. 
Other than that, is there anything I can do to limit feed costs? I want to free range because it’s good for them and they like it, but I live next to a main road. It doesn’t have a high volume of traffic, but still. I have almost two acres of land, but it isn’t fenced and I have a creek in the back. If they get into the creek I wouldn’t be able to go after them to get them back, and there’s a horse ranch behind the tree line at the back of my yard, and I wouldn’t want them to go there either. Also, a couple of my neighbors have dogs that hate other animals. It’s winter, the the tractor is stationary for now.