We made our own bait containers from buckets. Drill a 2" hole in the side real low. Wedge a wood board into the inside bottom. Buy "Tom Cat" brand bait chunks. Take long screws with a semi large washer and fasten the bait down thru the hole in the bait to the wedged wood in the bucket away from the hole drilled in the side bottom. You can place several baits in one bucket. I placed 2baits in ours and made several bait buckets. Placed them around our coops.
Store bought bait houses are exexpensive, ours were free from utilizing stuff we already have laying around. The cost of the pail of bait was our only expense. Keep a container of water close by that the birds can't access. The bait will make the rats incredibly thirsty and that is where you retrieve their dead bodies.
The first night we made ours, half the bait was gnarled off and the next day after we started disposal of the dead rodents. An economical solution for an expensive problem. Good luck.