To be honest: It mostly depends on your location. So we don't know.
Within Europe shipping usually should use the fair European rates but the only way to find out about this is to fill a Lulu shopping cast as a test and look at the shipping costs.
A simple estimation for an upper limit (assuming the hardcover print options) would be to add two books of http://www.lulu.com/shop/alexander-zalud/encyclopedia-desaria/hardcover/product-1393887.html to your shopping cart and then check the shipping costs when checking out (you don't need to buy it). But this book is hardcover, created in Germany and larger than 400 sizes - so it should be a good upper boundary for shipping costs to your location.
For softcover shipping costs you probably could put a maximum of three of http://www.lulu.com/shop/jürgen-mang/das-weltenbuch/paperback/product-5432082.html into your cart and then check the shipping costs. It's softcover, created in Germany and again larger (with three items) than the two ADOM RPG manuals, so the guess should be quite good.
Nonetheless we have to stress that in the end Lulu is responsible for the shipping costs.