Thanks to #SPARC ( @sparc) for this new "Guide for Authors Complying with U.S. Federal Agency Public Access and Publisher Policies."
https://sparcopen.org/our-work/guide-for-authors-complying-with-policies/
Bottom line: Compliance with the US federal #OpenAccess policies is free of charge. Publishers who charge fed-funded authors a fee to make their work OA are charging to publish in their journals, not charging to comply with fed policy. You can publish elsewhere and avoid those fees.