You'd be surprised actually. Once you factor in network costs, running your own on AWS is only ~50% cheaper than paying for SaaS.
Factor in the opportunity cost you pay by having to have a person manage a self-hosted CI/CD cluster rather than outsourcing it, and SaaS CI/CD is around 3x better value than self-hosted.
Happy to share more detailed numbers if people are curious...
But for 99% of people it doesn’t matter because their usage never goes over the free allowance anyway.