How do I allow anyone to edit a post — but not access dashboard

A combination of the S2 Member Plugin along with something like Advanced Access Manager would probably work best for you. You can set up subscriptions and pages access in S2 Member, and use Advance Access Manager to adjust roles/access or create new roles. (AAM is perhaps less functional than the ones you mentioned, but WAY easier to use, and will do what you describe)

S2 Member – http://wordpress.org/extend/plugins/s2member/

AAM – http://wordpress.org/extend/plugins/advanced-access-manager/

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