This is a social sciences problem, not a large player vs small player problem. At Sage, which is one of the largest social science publishers, we also lose money on social science OA publishing. We've tried for years experimenting with different APC prices and have struggled to figure out how author pays will work in the social sciences. Shoot me an email (details in profile) if you want to chat about this stuff more. It's rare to find someone with experience doing social science OA publishing on HN!