Get Series 1 DVD on amazon quick!
I don't check every shop and online DVD stores, but this much I know:
High Street Shops (that I've seen it in) - £24.99
play.com, sendit.com and choicesdirect.com - £17.99
amazon.co.uk - £7.97!!! WHAT A BARGAIN!
My copy just came in the post today! I don't know how much longer it will be at this price but I advise anyone who wants it to go and get it NOW while it's mega cheap. Their prices change all the time.
Happy shopping!