I have a nightly software build of a piece of software that takes 6 hours to create a 70GB artifact. The build process requires a GPU so it runs on my own HW. That's ~180 hours per month for this job alone. Is that really so hard to imagine?

I think you significantly underestimate the number of CI minutes people are using in practice.

(Which, yes, has implications for energy use/climate change too for sure).

It doesn't look like i currently have access to the usage data on any of the lots-of-runners-lots-of-PRs projects I currently work on (which are still probably way less than some large companies).

per minute billing is hard to wrap around the head

On my larger organization, we have on average 20 to 30 *active* runners during business hours. Assuming 5 on the off-hours, my napkin math says it comes down to about 10 fully-utilized-runners per month, so about 864$/mo. For the size of my organization that is honestly totally acceptable.

This is assuming 0.002$ per minute of job being actively executed. If it turns out to be 0.002$ per minute of *runner being registered* on the control plane, it would increase quite a bit. We are still using the old HorizontalRunnerAutoscaler with actions-runner-controller, with quite a pool of prewarmed runners idling to pick up a job. It would be a strong reason to use the new RunnerScaleSet (to take advantage of the reactive webhook-based scaling) and keep a very lean pool of prewarmed runners.

It could be 1 dollar a month, I'm still not paying to use my own ressources

Doesn't this depend a lot on how long your actions run? Like, you may have already invested in your own hardware (maybe because your actions use a lot of resources and it's cheaper) and now you have to pay per-minute of action runtime for the API that does the bookkeeping?

$3 gets me 730 hours of comparable Vultr VPS time.