In my opinion there will not be a rational supply and demand pricing structure for e-books until the format as a percentage of the total sales of books grows enough to be a significant fraction of total sales. As it stands now the pricing for e-books is pretty damn arbitrary in relation to cost. This will be especially true for older books pre-dating the era when it could be anticipated that books would be delivered to the publisher already in electronic format. It is actually a higher cost for a source to produce an e-book for such an older title than it is for a newly released book.