I have just started to study the history of Islam and having worked my way through some disappointing books I came across the following authors; Patricia Crone. Fred Donner. Christoph Luxenberg. Many of their books were offered at stupid prices. Why?
Usually, obscenely expensive titles are obscenely expensive because of the following:
Out of print
Very limited run
So few copies in circulation that there's a limited supply, sellers can charge what they please.
A cursory googling of the authors you've mentioned, all three of them have texts related to Islam on Amazon, and all are under $100. Most are under $50. That's not an obscene amount to pay for a specialized text by an author that's known to do good work in their field, by any stretch.
If it makes you feel any better, Dolph Goldman's The Grand Old Lady of No-Man's Land about the Vickers gun runs about $800 on Amazon, and Allan Williams' The Knight and the Blast Furnace (excellent text about the metallurgy and development of medieval armor) runs over $400.
I understand your comments but how long does copyright last before an economically produced re-print can be printed? As an aside is there anyway that answers can be automatically sent out?