it sucks that you can't carry on your paddle. isn't it sad that a paddle can be considered a weapon... haha...
here's my two cents: if it's not a padded paddle bag the airlines will not take responsibilty for it. as a matter of fact even if it is padded they won't take responsibility for it (cheap skates). they will make you sign that waiver regardless. there is no extra fees that i know of to check in sports equipment.
the only bag i know that is travel friendly is the really expensive Typhoon 8 full length multi-paddle bag that fits 3 paddles.

i have a pretty cheap paddle bag which i used for my CF. what i did was wrap my CF blade and the shaft with bubble wrap before putting it in the paddle bag. make sure they put the bright orangy red FRAGILE sticker on your paddle bag before checking it in and tag it with an address tag. hope that helps.