Hugh Houlgrave, who runs Houlgrave's books and rareities in Barovia, sells paper at 20gp a sheet.
This is pretty pricy, but not a bug.
However, I'm pretty sure he was selling it at 20gp per sheet before I put points into appraise and before I took the first merchant feat - Even a 5% reduction in price should mean they're now 19gp each.
Is he correctly programmed to take Appraise/Merchantile feats into account?