Right now we are shipping books via paypal but having the customer contact us with their shipping info. We then use the Canada Post shipping calculator to determine the cost of the package. The problem is Canada Post varies their shipping costs depending on where you live, rather then a flat rate per ounce. Averaging the cost of shipping seems like the way to go. Something like $1 (per ounce) domestic and $1.5 international. Then when I create the buttons for the books I just come up with the weight of the book. Is this something you have seen with other users?