Happy to answer any questions about it. We've been using Buildkite for a while - it has been a pleasant experience and has let us craft a CI setup whose cost would be prohibitive to us otherwise.
Another similar option we tried is AWS CodeBuild which has per-minute billing and provisions the build machines for you. However, it's very bare-bones and because you always get a from-scratch instance for each build you have to distribute your docker cache which is not ideal.
Another similar option we tried is AWS CodeBuild which has per-minute billing and provisions the build machines for you. However, it's very bare-bones and because you always get a from-scratch instance for each build you have to distribute your docker cache which is not ideal.