Having purchased comic and other art from different European art auctions and houses and then shipping to the US, the "rules" vary dramatically.
Shipping is a small part of a much bigger equation that can involve exchange rates, fees, commissions, fees on exchange rates, wire fees, credit card fees, international bidder fees and even VAT, regardless of whether you think it should (or really does) apply or not. For shippers, I recommend Fedex or DHL international - if those options are available to you through the auction house.
I highly recommend reading the fine print and even going so far as to confirm with them directly.