Rare, certainly: there are plenty of vanity publications that were chucked into the bin by almost everyone who was unlucky enough to be given a copy. Precious? Well, with the help of an electronic friend I found ISBN 978-3-8365-7349-8. Apparently a copy of that book is worth about £40k. Can anyone beat that?

(EDIT: I'm assuming "precious" means the same as valuable here to make the question easier to answer. In fact, of course, people usually say "precious" when they mean a personal or emotional attachment or cultural importance rather than economic value.)

I’ve not followed the market much but I suspect some fine press editions of Stephen King’s work would be up there. Of course, tons of standard paperback editions of those that could be pulped.