I know!!! Costco sell them much cheaper than anywhere else but only in the summer as they are sold there with the garden furniture.....strange, yes, but true.
You have to join or get a card from somebody. There is one in Manchester, Liverpool and Bushey Hertfordshire and possibly elsewhere and they are an American cut price outlet place. They are still quite pricey, but definately cheaper. I had a good look at them and very nice they are too, though I use a couch myself so haven't got one.