If you look around, there are a lot available for under £10, especially with the Classic stuff (Bambi, Mary Poppins, Toy Story etc). I don't think we're allowed to mention most of the cheapest places to buy them, as I believe they're all competitors.
Most of the new ones are cheapest in supermarkets, in store, but you'd need to look around to see which is where, as they keep changing the offers.