that would still pose a problem, not cost-wise, but you'd still need to download image after image. Will a single instance be capable of "downloading" all existing images every 6 months?
None of the big providers offer always-free VMs, but if you could just ping the registry endpoint, Lambda might be able to do it since you get 3.2 million seconds of compute "always free"[0]. Same for Google Cloud Run, although it's only 1GB egress a month[1], and Azure Functions[2].