I stopped by Pearson Education's booth at a recent statistical conference (JSM) and asked for the prices of their introductory statistics textbooks. They didn't have such information on hand and seemed surprised that I asked. That was disappointing, and, with such a large organization, it was difficult to believe the lack of pricing information was an accident.
The free market works when supply and demand are in balance. Suppliers develop or manufacture materials and products, and they choose prices so that their products compete for the attention and dollars of consumers. It's a straightforward system, and it is often incredibly effective. But this is not the way the market works for course textbooks.
Students do not choose which textbook offers the best resource for the price. Rather, teachers do. Market fundamentals do not function when the end-consumer does not choose which particular item they purchase. This doesn't mean teachers should switch to a model where each student selects her own textbook (that would make for an unmanageable course), but it does mean teachers should pay close attention to price to help rebalance the market.