I’m a big fan of dell wyse machines. Loads on ebay, ex business machines. X86 so decent support, decent dell power supply, on / off button / in cases and low power.
I have wyse 3040 for pihole cost 39.99
I have wyse 5070 with windows 10 for plex and running a Ubuntu 22 server in virtual box, cost 59.99
https://www.parkytowers.me.uk/thin/wyse/3040/ https://www.parkytowers.me.uk/thin/wyse/5070/
Both mine are there and tested for power use.
Running 24/7 for a good 6 months. Certainly not noticed any difference to power cost.