local ads/classifieds. Ebay Kleinanzeigen specifically, if you're in Germany

But in general, get a used one, preferrably fetch it yourself so you can check it's working. Get S9i or S9j, installs Braiins Firmware and be happy. Avoid S9k because Braiins doesn't run on that revision.

Then have 1k-1.4K watts ready and enjoy being naked in your trailer, because it will be warm haha

Aaand, either be resistant to tinnitus or perpare to build a "silencer box"