Hi Dave! Thanks for the compliment. :-D
After looking at postal rates online, you may change your mind:
First Class International: $11.39
Priority Mail International: $28.75
These prices are an estimate based on 15 ounces in a 14" x 1" x 1" shipping tube. I won't know an exact price until the posters are in hand but at least you get a general idea ... they probably won't be that heavy.