Anyone knows where to buy a cheap Linux box?

You're limiting yourself a lot by expecting Debian preinstalled. If you're going to deploy homebridge / ha on it, you really should be able to install the whole system yourself. I don't expect you'll find anything preinstalled really and I wouldn't trust them without wiping anyway.

For the hardware itself, check for office mini PCs on eBay. Optiplex or thinkcentre are common ones that get sold cheap after 4-5 years. NUCs are fun, but usually more expensive.

A random eBay mini PC is probably going to be a good option.

You'll have a full GUI install process that's pretty trivial so it's probably not worth looking for something pre installed.

Home Assistant likes to write to disk a lot last I checked, so you'll probably want a decent sized name brand SSD.

NUC, BeeLink PC etc are all great small form factor but you will have to put Debian on yourself.

If you want to run Home assistant the answer is proxmox If you run zigbee then run a separate MQTT instance and get a ethernet zigbee dongle. (You can run MQTT and in HAOS, works till you need to downgrade one, or restore one, and not the other).

I would also think about building an AM4 box, one with dual PCIE slots and some SATA ports. Local LLM, NVR processing, mass storage etc... Your gonna either end up out growing the nuc or want something more serious down the road. AM4 boxes are cheap (sub 300 bucks) and opens up more potential in the future.

Dietpi[0] is a pretty good minimal debian-based distro that works out of the box with almost no configuration.

It was originally designed for a RPi's (I think), but it's expanded to tons of other devices. Here you can see a benchmark of each supported device and decide yourself what you want to go for[1].

0: https://dietpi.com/#download

1: https://dietpi.com/survey/#benchmark

Just get anything Intel-based and install debian yourself (AMD stuff should probably be fine too, but I'm not sure if newer (i)GPUs are all fully supported, and Intel seems to have cornered the compact PC market). HW support is extremely broad these days.

Choose the computer with the most-supported peripheral hardware. Not some weird peripheral chip. You don't need to be mucking around supporting some unusual WiFi chip, for instance.

So, that's generally an Intel-Chip based machine.

Myself, I am partial to Lenovo hardware, with Intel-based peripheral chips. I usually buy them new from Lenovo* and customise the build. But then, I'm flush enough to do that. YMMV.

* Current machines: P53 laptop, M70T desktop. With LinuxMint installed by me. Throw away the Windows installation. It's done its job nicely, by giving you a subsidised set of hardware.

You could go for a Fujitsu Futro S740. Costs around 70 Bucks and often comes preinstalled with Proxmox (which is Debian under the hood), depending on the seller :-)

I used a nuc-sized computer and installed debian myself.

I find these[1] great for headless, one wire (w/ PoE hat) Ethernet services. Wish there was a nice enclosure available.

[1] https://radxa.com/products/zeros/zero3e/

I found some Beelink Celeron based systems on Amazon for less than USD200. 16GB RAM, 512MB SSD, Wifi 6, etc. Performs massively better than my Raspberry Pi 4 with 8GB.

It's very simple to download Debian Bookworm and make a bootable USB stick. Takes less than hour to get the system installed and up and running.

There are a bunch of cheap mini PCs on Amazon.

Most of them are going to come with Windows pre-installed, but you can wipe it out and throw Debian on there. That will be much easier, and cheaper, than trying to find it pre-installed.

I just threw Mint on a Beelink mini pc I got for about $170.

https://www.theserverstore.com/dell-precision-t3420-sff.html

I use these little ones (many options... some at < $30. 2"x2"x1"). Low power consumption, budget-friendly. www.friendlyelec.com