It's not just about the monetary cost. It's about the environmental cost as well. Why do we think we have the right to kill wildlife? That line of thinking is why there are so many animals either extinct or on the verge of. But they all play a role in the ecosystem, so we're only shooting ourselves in the foot by eliminating predators. Case in point: killing the wolves that sparked the explosion of deer, deer damage on forests, deer-borne diseases that they give to people via their ticks, deer totaling cars on roads... etc. It's all connected. If it's too expensive to protect your chickens, then don't have chickens. If you have to have chickens, then have a large flock so you can sustain some loss and still have more left.