One of the reasons I'm still using GitHub for a lot of stuff is the free CI, but I hadn't really realised how little that actually costs. For #CHERIoT #LLVM, we're using Cirrus-CI with a 'bring your own cloud subscription' thing. We set up ccache backed by a cloud storage thing, so incremental builds are fast. The bill for last month? £0.31.
We'll probably pay more as we hire more developers, but I doubt it will cost more than £10/month even with an active team and external contributors. Each CI run costs almost a rounding-error amount, and that's doing a clean (+ ccache) build of LLVM and running the test suite. We're using Google's Arm instances, which have amazingly good price:performance (much better than the x86 ones) for all CI, and just building the x86-64 releases on x86-64 hardware (we do x86-64 and AArch64 builds to pull into our dev container).
For personal stuff, I doubt the CI that I use costs more than £0.10/month at this kind of price. There's a real market for a cloud provider that focuses on scaling down more than on scaling up and made it easy to deploy this kind of thing (we spent far more money on the developer time to figure out the nightmare GCE web interface than we've spent on the compute. It's almost as bad as Azure and seems to be designed by the same set of creatures who have never actually met a human).
