Here's an interesting how-to: The U.K.-based Association for Learning Technology has published a guide (.pdf) to changing a journal's business model, including moving it to an open access model. The authors explain their motivations in the abstract:
Hundreds of societies publish journals in collaboration with publishers. Some may be considering how and whether to renegotiate or go out to tender. Some may be considering whether they can/should/wish to change the business model of the journal (e.g. by a move to Open Access). Other societies may be considering using an external publisher for the first time. This guide, based on our experience, is written for all of these.
Via Boing Boing