ARL has released "Funding Article Processing Charges, SPEC Kit 353, Published by ARL."
Here's an excerpt:
The Association of Research Libraries (ARL) has released Funding Article Processing Charges (APCs), SPEC Kit 353, an exploration of the strategies that ARL member institutions are using to address APCs. This SPEC Kit covers how the funds are established and how they are handled (e.g., policies, applications, budgets, administration, outreach activities, etc.), sources of funding, and whether and under what circumstances libraries are partnering with other units (or other libraries) to fund this aspect of open access. . . .
Read/download SPEC Kit 353.