A dollar or less...
My reading of Tribes is now available on iTunes as a three hour audio book for less than a dollar. (update: now the bestselling audio book in the world. Price matters, apparently). [You missed it! It seems as though it's now $6. Still a bargain...]
Or, if that's too much, Audible is using the audio book as a freebie promotion, but I think you need to register.
The souvenir, dead tree, printed hardcover edition is easier to take to the beach (B&N). A Kindle edition just launched. More versions than one could ever hope for.
