buy a dc version of asrock cpu on board ( i have 3 Q1900DC-ITX that i bought 8 years ago and run 24h and still working ) on aliexpress you can found used for like 30euro

• you need a dc (you can found for like 10 or 20euro)
• you need ram (can found for 10 euro)
• you need a hd or ssd ( 10 euro )
• you need a cable that give power to your sata hd (3 euro on aliexpress)
• you need a cable for power on the mobo ( 1 euro )

ok now you have everything you need for your server. fanless, 20 times more powerful than a rasberry.

I use arch linux and i have fun