ECR is kind of hard to beat if you're ok with being in the cloud.

The last time I used it earlier this year for a company already on AWS, it was ~$3 / month per region to store 8 private repos and it was really painless to have a flexible and automated life cycle policy that deleted old image tags. It supports cross region replication too. All of that comes without maintenance or compute costs and if you're already familiar with Terraform, etc. you can automate all of that in a few hours of dev time.