A few weeks ago I went to my local (and ridiculously expensive

) used bookstore and found an original, first-edition copy of Bachman's "Thinner" in hardback. Supposedly original copies of Bachman's books are worth a lot of money (except The Regulators, since that was printed later.)
Any of you collectors out there, how much do you think this book is worth?
Edit: Also, the book is in good condition. The jacket's torn a little bit in some places, but the rips are at most a quarter of an inch long and few and far in between. All of the pages are attatched and the book itself is in near perfect condition.