Open Access journals need to finance their existence; some do this by charging a fee to cover the publication costs. The publication fee is often covered by the institution or by the research grant money.
As the amount of Open Access journals grow it also becomes important to have different strategic advantages. PeerJ for instance a journal we have discussed earlier give the authors choices on how to pay for the submission.
Collabra is another new example on how this can manifest. They recently launched a journal with a payment model that give some of the publication funds back to the editors and reviewers in the form of credits. The credits are awarded for helping out with the peer review process and can be converted to value either in money or by donating it back to the journal or to other open access funds that help authors with the publication cost. You can read more about the actual sums at “New open-access journal plans to pay peer reviewers“.
Hopefully this new strategy will work to draw qualified reviewers and more high quality articles to open access alternatives and not further inflate the publishing cost by adding extra expenses.