easibed (the horse stuff) costs me £8 a bag and lasts at least a month for two largish houses with 7 in each and two smaller ones with 3 birds in each. I put it in the laying boxes plus a bit on the floor of the house. It dries up poop, doesn't fly everywhere, smells quite nice and they like to scratch around in it. I don't use with the horses funnily enough as its heavy to lift when very wet-although I did use it with some success in a stable used as a field shelter.
I preferred the easibed to shavings for the chickens-less dusty too. Have also tried cardboard which was OK but flew round the garden a bit and worked out more expensive. When I move I'm going to use sharp sand in the bottom of the houses, easibed in the laying boxes.