Raspberry Pi as Forgejo Runner
In my instructions on how to setup Forgejo with a runner, I used a Hetzner server for the runner. This costs roughly 5 euros per month, so 60 euro annually.
A full Hetzner server might be a bit overkill for a simple runner. Especially if you are just running Shell scripts or static site generation. The Hetzner server supports things like high bandwidth, low latency, unique IPv4 address, high uptime guarantees. Most of these are not necessary for your own runner.
Therefore, in many cases it's probably a good idea to run the Runner on your own hardware. What I have tested and works for me is to use a Raspberry Pi 4 with 1 GB RAM and a 32 GB Class A MicroSD. At the time of writing, the price for these was €44 for the Pi and €10 for the MicroSD card.