Yeah, your goal is pretty nice if you want to open source blacksmith at their level, but I think most people would be pretty happy with just a hetzner vm using act https://github.com/nektos/act if they want github actions, or jenkins.

I think we can rent hetnzer vms on a per hour basis or maybe we can't , but I do know that there are services like (linode?) I guess, which use a per second model.

Combine that with I think automatic installation of act and you pay for per second use of your CI.

Plus points if we can use criu to scale from lower end machines to higher end machines depending upon the task while continuing the task from where it was left.