What I've seen is that the binding is different for international editions - paperback vs hardback, usually. That would account for the difference in price.
A bit of an old post here (and I suppose a weird first post, but, eh).
The difference in cost to the publisher for hardcover vs softcover is roughly a quarter. Not a quarter of the price: 25 cents.
But we've been socially programmed to think of them being worth far more, so we all assume the 300% markup is reasonable.
And I'd do some checking when buying International versions-I've run into a one that a little research showed was significantly different than the US version. Annoying since that ended up being a $165 used US version book vs $50 new international =x