A PayToUpgrade plugin supporting corePHP's Community ACL component was finalized yesterday and will be available soon (screenshots below). Utilizing the easy to configure upgrade plugin system of PayToUpgrade, Community ACL joins Dioscouri's JUGA in now having the easiest way to charge user's for different access levels on your site.
Of course, if powerhouse ACL isn't required for your site, remember that P2U comes with a standard Joomla user ACL plugin as well!
As with all PayToUpgrade integration like Mosets Tree or core content, no modifications are required to Joomla or the components themselves.