You can quite easily plug in your own CI runner on Github and reduce the cost by 20 times or more, especially if you're already running k8s. (I wrote a post about it for the cheap managed k8s service I built https://symbiosis.host/blog/using-actions-runners)
I use ARC and I wouldn’t call it trivial to set up. Took awhile to tweak all of the things necessary to get it working right. It is way cheaper though once it is working
