From Shawn Lawton Henry:
The Web Accessibility Initiative (WAI) Education and Outreach Working Group (EOWG) has published Developing a Web Accessibility Business Case for Your Organization
The 5-page resource suite describes social, technical, financial, legal and policy aspects of Web accessibility. It is designed to help organizations develop their own customized business case for Web accessibility. It provides text that can be used as is, as well as guidance on identifying the most relevant factors for a specific organization.