Christine Fruin and Fred Rascoe have published "Funding Open Access Journal Publishing Article Processing Charges" in College & Research Libraries News.
Here's an excerpt:
Libraries are viewed as the primary resource at academic institutions for information on scholarly publishing issues, including OA. Faculty interest in OA publishing is increasing, and when recent federal mandates for OA are implemented, the interest from those doing federally funded research will grow quickly. As such, librarians should be prepared to answer questions from faculty and researchers on how they can cover the costs that are often attendant to publishing in OA journals. While librarians should advocate and educate their constituents on the availability of green OA and the cost-free options available with many gold OA journals, they should also be cognizant of the frequency at which faculty and researchers are publishing in gold OA publications that charge a fee and the available options for covering those costs.