look at it this way. if you wanted a new top of the line DLRS and a 400mmf4 or 600mm f4 lens you will be in for like $10,000 or so. AND you can buy as many as you want all day long......so a couple of grand for a "rare" (relative) lens is not so bad.
collectors by mint stuff for the most part. so the 3b that sold for 3000$ that did not even have the flange or waterhouse stops was probably NOT bought by a collector