They get cheap shipping prices because they send out stuff in bulk and can get a sweetheart deal to ship with X instead of Y.

$40 to ship international sounds like an amazing price, but as others have said if this book has real value you don't want to skimp on the shipping. If that thing goes missing and you don't have any insurance on it you're out the value of the book.

If you are looking for a good deal you should be shopping around. Check FedEx and UPS, they might have decent prices.