Not sure of what current prices look like but an old desktop sitting on the floor of your office might work well for you. You would need decent internet but running a single node kubernetes cluster as a GitHub action runner has worked well for others I know.

A buddy of mine runs his whole CICD setup off an old gaming desktop. They use tailscale to connect to their hosted infrastructure and set it up as a GitHub action runner.

For a solo dev this might be the way to go.