The great thing about addall.com is that you can specify where you are in the world and it takes into account shipping costs. For me, shipping costs for single, second hand, books are routinely more than the cost of the book so this is really useful. They then go one stage further and allow you to specify which currency you would like the costs displayed in.

Perhaps www.pagesonpages.com will add similar features in the future, it can't be a simple thing to do but I appreciate it.