A Guide to Rare Books?

I was wondering if there was a serious guide out there that gives some
indicator as to the value of rare books, perhaps a speculator publication? I
am looking for something that goes beyond the simple value of first edition
STephen King novels and explores the values of very old books, dating form
16th century and earlier, into antiquity. Perhaps it also outlines current
collections and their worth?

I would assume there is something like this, and I'm interested in knowing
if it exists and where I might find something like it.

Thanks