The Aubiose website has a list of suppliers here
http://www.aubiose.co.uk/stockists.php
If one is near enough, it would be worth getting a couple in the car and not paying delivery, unless delivery is practically free, like my stockist. I do think that £13 per bale is a very high price to pay, plus delivery. If my supplier can sell it at £10 delivered, some people must have very high profit margins on it.
My run is 12 sq metres and I reckon to put down 3 bales when it's empty and swept, ie about a bale per 4 sq metres, to give 4 inches deep, soft and warm for them to sit on and dig in. I stack the spares round the edges, against the winter tarpaulins, good insulation, which doesn't reduce floor space as the girls can sit up on them. During a year, I probably use 2 bales in the coop, which go on the compost heap as they end up 50% poo and thus are a very good accelerant and fertiliser for compost,esp. If mixed with grass clippings etc. Another bale gets used as top up on the floor when it gets a bit thinned out by poo picking. I've found that Aubiose lasts longer if you put it down quite thickly to start with, and of course if it's in a dry covered run. Any poo I miss because it's been scratched in becomes totally dessicated and eventually becomes powdery, and doesn't smell and is inoffensive. Over a permeable membrane, at least no earth gets dug up into it to make it dirtier. So £60 a year for six bales = £5 a month, not too bad for six hens,
The hens don't appreciate my efforts changing the bedding as the new stuff goes down all white,whereas the old stuff had gone brownish with age. They're very suspicious of the change in colour to their living room carpet!
