WH Smith's UK ebook store at
http://ebooks.whsmith.co.uk/ has 50 % off their top 30 fiction, nonfiction and business epub ebooks. Most title are in epub only but some are in multiple formats.
I picked up 2 non-fiction and 1 fiction ebook for less than 11 GBP.
There is no problem with people outside UK buying them but the secure checkout is a little quirky in that you have to fill out all address fields for the order to be processed.