I just received a book from LCV (my Christmas present from my wife - I don't know which book it is as I have showed my wife my wanting list, but the package was rather heavy - I will tell it once Christmas will be passed), and postage was only 6.50 euro for sending from France to Belgium.
(it was send as "colieco")
The perception of the postages costs depends naturally of the value of the book. 6.5 euro for a book of 20 euro would be perceived as very high, while for a book between 50 and 100 euro it will be seen as moderate.
Postage from Belgium to other countries in Europe is quite higher than in France.
Postage tarifs in France can be seen at the following link