Look into a NUC on ebay. I was able to snag a new 11th Gen i3 for 200 eur. Power draw is about 7w with a headless Debian. Running a media server, nextcloud, pihole, an arr stack and I'm planning to add home assistant and a zigbee bridge which I now run on a pi.
If you aren't planning to run to much on it a rpi4or5 will actually be enough and these things can draw 15 on absolute max load.