It still looks free:
https://github.com/Cisco-Talos/clamav-devel
That's licensed under GPLv2, available for download without any kind of key/password, and includes build instructions. The poster on mac could even use homebrew to install it with one command.
And they even include instructions for mirroring the signatures here:
https://github.com/Cisco-Talos/clamav-faq/blob/master/additi...
What part of it requires payment?