I use plastic organizing bins. They come 3 for $1.00 at Walmart. I would've preferred the wire mesh, but those were $2.00 for only 1. I attached them to the cage a little higher than my rabbits backs with wire.They work great and even though they're plastic, my buns haven't even scratched them up. And my Rex buck really tries to do that, too. lol
You can sort of see them in this pic.