Well I know they're usually around $80-$90 at the brewery, and are pretty limited in terms of bottle count. On top of that, they're a complete bitch to ship. Trade accordingly :-)
I would think box size, not weight/cost, would be the main factor here. You'd have to have a huge or long box, then make sure it's given bomb-proof packaging. If it breaks, you're probably not going to be able to replace it.
You can get a 3L wine bottle shipper ( around $10) and put that inside another bigger box. The weight of 3L alone comes out to near 12 lbs.
