A nonprofit group called Knowledge Unlatched, has come up with a new model for publishing open access books. In this model, libraries pick titles they would like to be open access and pay a title fee for each of those books. Those fees are meant cover the cost of publishing each book. The books are then published with a Creative Commons license and made available DRM-free via OAPEN, the HathiTrust and eventually the British Library.
For more information about this new OA model for books:
Knowledge Unlatched: http://www.knowledgeunlatched.org/