I recently got most of the Lost Era books off of Amazon's Marketplace. All of them were under $0.10 (plus, of course, the $3-4 shipping), and I was pleased with the quality. There are cover creases on the spine, but the binding's well intact. Some of the pages are a little warped, as if they've been exposed to moisture, but there's not a single one I'd send back because of lack of quality. (And I would tend to say that most sellers' evaluation of mint/near mint/etc. isn't graded with nearly the precision of, say, baseball cards. Just avoid the ones that are "fair" and below.) Occasionally, I've even had a seller throw in a freebie like a good-quality bookmark, which is always a pleasant surprise.
And, yeah, they're making the money off of shipping. Anyone who's ever sold on eBay could tell you that. My guess as to the cut that eBay or Amazon takes goes towards pure profit.
This thread reminds me...I need a new copy of Masks, as my first finally mostly-disintegrated. And, fortunately, Amazon appears to have nearly 100 copies.