This is one of those Dvds that you'll rarely see under a tenner. Amazon and Play have recently reduced it, however, Play is 1p more and the dispatch time is 1-2 weeks.
Next best after that is £11.89 at Sendit.
IMDB users have rated it as the 14th greatest film of all time. http://www.imdb.com/title/tt0047478/
Classic Japanese cinema which was later remade in to a little known Hollywood film called...The Magnificent Seven.