Picked up the 50 book collection for me youngest for just 20 nicker today. Had wanted to get them online from the book people at £30 a box, but this is an item that's always out of stock.
You'll need to buy this somewhere that the book people deliver to, or have some sort of concesion. They sell stuff via the little shop where I work and I know they do this with lots of other workplaces etc around the UK so good hunting. The packs are pre-priced, so the £20 sticker wasn't a one off.