I don't know where you are in the EU but UK refurbishers constantly sell post-lease desktops and laptops on ebay for around £50, shipping to any EU country is usually £10-20 on top of that, if anything.
Is plentiful and easy to buy, again - ships anywhere in the EU.
As for the power consumption - I have to disagree again, I have an SFF like this and in idle it uses about 10W of power, 40W under load.
Rpi4 4GB uses 1-3W in idle, and up to 15W under full load. Yes, the numbers for the Pi are lower, but I wouldn't say "it's not even close". It's close enough that I would absolutely consider getting the larger PC instead.
Like this kind of stuff: https://www.ebay.co.uk/itm/HP-Lenovo-Intel-i3-Dual-Core-i5-Q...
Is plentiful and easy to buy, again - ships anywhere in the EU.
As for the power consumption - I have to disagree again, I have an SFF like this and in idle it uses about 10W of power, 40W under load.
Rpi4 4GB uses 1-3W in idle, and up to 15W under full load. Yes, the numbers for the Pi are lower, but I wouldn't say "it's not even close". It's close enough that I would absolutely consider getting the larger PC instead.