I don't use much of CloudFlare services but it seems kinda cheap, $0.015/GBmonth for storage (+10GB free), Workers are charged per request and CPU time, both of which would probably be quite low for a registry so free plan would go quite far?

I just set up the official registry on a VPS (for similar usage pattern) and it was a bit of work and probably much more expensive, this seems quite attractive unless I've misunderstood something.