You have to have a Red Hat login at redhat.com in order to get to the download page:
https://rhn.redhat.com/rhn/software/...pportedISOs.do
To the best of my knowledge, you actually pay for the support, not the bits. I test with Red Hat 6.3 (unsupported) by adding the contents of the DVD to a repo, allowing me to use yum to install additional programs.
CentOS is probably the next closest (as previously mentioned), and you can use the online repos for free.