Yes its way too expensive. When I find something I need I always try to purchase at least 4 extra cards to on sell, just to lessen the postage sting. Or, if its only one card, I use comc mail box. This brings the vost way down, but still not cheap enough.
COMC mailbox is great, but they will charge you $2 to process the cards (up to 4), $0.50 for each additional card. I am reading about this other mail forwarding service that is not card-specific called MyMailbox, looks promising... $0 processing fee as they don't scan the cards, but offering relatively cheap repacking options for bigger items that are not necessarily cards.
I use COMC mailbox a lot. Even with the $2 processing fee it's cheaper providing you send in bulk. I probably have my inventory posted to me every 3 months and with a lot of 150 cards or so shipping is around 80cents each including a toploader for every card.
It's also helpful for those sellers that won't ship outside of the US.
Thing I hate most is when a well meaning seller sends me an additonal 20 junk cards. COMC process those as well at 50 cents a card and there's nothing you can do about it. 99% of them are rubbish you can't even sell on.