Hi TSGoons, and welcome to MobileRead.
I use the ebook price comparison site
www.eBookPrice.Info to search for ebooks at the best price.
Their collection of eBook stores that it searches has grown considerably.
Click on the Union Jack if you are not quoted in £.
Your examples:
I'm not sure of the geographical buying restrictions at all stores but I have seen mention of work-arounds on the forum.
I hope this helps.
WetDogEared