Buy European

Edit: somehow forgot that HA sell their own devices, HomeAssistant Green for 100$ and HomeAssistant Yellow which also supports the project.

Original comment: Highly recommend a used "enterprise mini PC" from Dell , HP or Lenovo. Get it from your local IT refurbisher, eBay or your local ebay-equivelent.
These are sometimes called 1L PCs for their 1 Litre size. Model names are Dell Optiplex, HP Elite desk or Prodesk, Lenovo Think centre. Prices are €100 to €1500 depending on age and specs. €150 should be more than enough for HomeAssistant.

Alternatively https://slimbook.com/en/ sells Linux PCs out of Spain, and https://www.tuxedocomputers.com/ out of Germany.

Another option is the british RaspberryPi, but that might be more hassle. You need to separately get a good power supply and cable, good SD-Card, case, maybe with fan. And its ARM not x86, but that doesn't matter for HomeAssistant unless you're doing something very exotic.

There are a lot of refurbished ex-corporate mini PCs (Intel CPU, 8-16Gb RAM, Windows 10) on eBay for around €100. It should be possible to install Linux on them.

Question of curiosity: why not consider RaspberryPi for the task? It is definitely going to be cheaper and more power efficient when comparing to mini computer (even if you take new one), because has so much more computing ability per Watt. I've been running HomeAssistant + cups server + small file server on RaspberryPi 3b+ without any issues for few years, and it was pretty actively used.

Additional point, RaspberryPi is publically traded company on London Exchange, and was founded in Britain, which mostly matches the "Buy European" motto ;)

Digitec/Galaxus Sells pretty much all the tech stuff amazon does but is a swiss cooperative.

Switzerland is part of EEA/European Market, so no tarriffs.

I went with a fanless solution, the Slimbook Zero, if that fits your taste.

One option is to look for used and repaired thin clients.

Not European so I can't answer that part.

If you are only looking at running Home Assistant, why not look at one of their own boxes? Such as the Home Assistant Yellow. Or maybe something along the lines of a 1 liter PC such as the OptiPlex 3070 or whatever the best bang for the buck is on eBay nowadays.

If you stick to official sellers and sellers with plausible-sounding positive reviews, AliExpress can be fine, and shipping is often quick, though warranty support is a bit of a gamble. There are loads of cheap N100/N150 boxes and other Mini PCs on AliExpress.

Have you looked on eBay? You can either get second hand from someone local to you like I did recently or a just check on who / where the item comes from before buying?

edit to add more clarity

Seen as this is buyeuropean and you may not want to give eBay its percentage what I meant by check on who / where the item comes from is using eBay as an aggregator, checking for sellers and then looking for their storefront outside of eBay to avoid giving them their sales percentage.

As others have said, a Raspberry Pi 4 or 5 will do everything you need for HA short of voice support.

If you do want to set up voice recognition, honestly, my first stop would be Wallapop/eBay. You can find something marginally more powerful than a Raspi that way if you don't mind the additional power consumption. Or, given what's out there, I'd try to put something small together as a bit of a project from used parts.

Have you tried https://www.pccomponentes.com/ ? You could try fnac too (although I'm not sure where are they from). There's also pc box I think. You might try your luck in those