Digital BW, The Print

How about numbering the prints, and then have pricing tiers such that 
the first X prints  of a given size cost Y, then next X prints cost Z 
(where Z is more than Y), and so on.  This has a couple of advantages. 
First, it motivates an interested buyer to buy sooner rather than later; 
it automatically makes you more money on the best selling images, it 
means that you won't have to keep printing one popular image ad nauseum, 
you won't have to ever deny a customer a sale because the edition sold 
out, and early buyers will want you to sell more images because it makes 
their image more valuable.

-Peter