You actually bring up another point when discussing the "true value" of used books which is the true value of convenience to many people. One could always find used books for 50 cents or less, it's just that your selection was often limited and it would take time to find what you wanted if you wanted something specific. The real value of a used bookstore was organization and reliability (not having to wait for the library's spring fundraiser, or for hand me downs from a relative, for example).

Frankly, although I see scores of books at Amazon selling for a penny, once one adds shipping to the cost, they run about the same as they would at one's local bookstore. However the convenience factor of being able to find a recommended book within minutes and buy it is very high. I see this as the major factor in the success of the Kindle, because it sure isn't an economical choice, and it's astonishing how many eBook users are unaware of free content.