The Rick Brant series sold close to 2 million books. If three quarters of those books were lost or destroyed that still leaves 37,500 of them out there someplace. Another wild guess of mine is that there are, at most, somewhere between 2500 and 5000 collectors of Rick Brant. I will grant that there are many books which are indeed rare. The Ignorance of Buyers.
Some sellers take advantage of the Myth of Rarity to charge outrageous prices.
If I priced my books this way my collection would be worth thousands instead of hundreds of dollars. Some of this may be ignorance on the part of the seller but there are sellers who are blatantly misrepresenting their books. Guilt by Association. Because some Rick Brant books command high prices, some feel that ALL Rick Brant books should be priced accordingly. This creates a cycle of increasing prices.