There are some solutions, but the incentives don't seem to be in place to encourage them. The best seems to be reducing the overall number of textbooks, allowing each one to have a larger run and thus to better benefit from economies of scale (and be cheaper to buy at the same profit margin for the producers). But to achieve that we would have to stop letting professors choose their own books, and professors are not known to appreciate being herded.
WHAT??? for example, stewart's calculus book has been used for twenty+ years all over the english speaking world. you find me a ny times bestseller that has had that kind of run
-- Richard Baraniuk, 2006 -- http://www.ted.com/index.php/talks/richard_baraniuk_on_open_...
So it's a bit more complex than that. It may be "economy of scale" in that a professor isn't going to take the time to write a solid textbook without being able to make back at least his expenses. But if we had some way for people to collaborate more easily and cheaply to write a textbook...