I don't want to be a negative nancy, but at least a few of those are under $12 brand new and shipped on Amazon.
yeah I checked the prices on Barnes & Noble too, and most of these books are $12-14 brand new. Only Real Food Daily was a bit higher at $16.
If I was selling off used cookbooks, I would not expect them to go for more than $7-8, especially ones that are paperback. The only exception would be if the books were in pristine condition (no smudges, tears, or food stains).