So, at the beginning of the lockdown situation I had a go at refurbishing an old corporate desktop class machine for use by a friend. This thing was an Optiplex 790 or some such tomfoolery, which was a first-generation Core i7 machine in the small form factor case (closer to a Mac mini in size, low-profile PCIe slots, etc.). It actually impressed me when it was done - it was a perfectly capable lightweight computing machine. My refurbishing extended to all of fitting 16GB RAM to the thing (it had none at the time) and putting Windows 10 on it (which activated with the 7 license it had - corporate desktop!), and even with the spinning disk inside as a boot drive, it's perfectly fine even for some rather older games, and handles basic tasks like web browsing and Office perfectly well. I did hold off on replacing the hard drive with an SSD, though - some quick looking showed that the price of doing that (even with how cheap SSDs are now) wouldn't have been a good idea.
The looking did give me ideas, though, as to what you can get for not much money. The dumb-no-longer-dumb-but-real-PC really started up as an experiment to see how cheaply you could build a decent PC, and that got pretty cheap but some more eBay searching and benchmarking indicated that you could do, perhaps, a bit better. So, I started looking at some of these business PCs, specifically the small form factor ones, and basically came up with this: for between $100 and $150, you can get a 3rd or 4th-gen Core i3/i5 system with some memory (generally about 8GB) and a spinning disk drive (usually around 500GB, though sometimes bigger or sometimes SSD), and it will likely have Windows 10 on it. That's a complete computer (unless you want to get a bit tetchy about it not having a keyboard, mouse or monitor). To put that into perspective, the new build involved a Pentium Gold CPU for about $70, and about another $50 on the motherboard, and that doesn't include even RAM or storage.
Prices spike after the 4th gen CPUs at this point in time, and systems with i7s in them come at a premium as well that I'm not entirely sure is worth the additional cost or jump down to a 2nd-gen CPU. (I'd rather have a i5-4560 rather than a i7-2660, personally.) You're also not going to get a real GPU most of the time with these - onboard or bust - and if you get an SSD, it's going to be a 120GB one. (I did look, and while I was more after a SFF system, a regular midtower doesn't incur a price premium, other than maybe additional shipping cost.) But, that's still a complete system, with a licensed and activated copy of Windows 10, for about $150. And, that's a fair amount of computer too - it's not going to be the thing you want to depend on to do your 4k renders for YouTube, but for most anything else it'll be perfectly acceptable. Even some software development stuff shouldn't be too hard to do on a machine like this.
I did end up putting a bit of money where my mouth is on this one, and I ended up with an HP ProDesk 600 G1 SFF machine. Spec-wise, this thing came with 8GB DDR3, a 500GB spinning disk (with two! empty bays and matching SATA ports for each, one of which a 2.5" one), a DVD-DL RW drive, a Core i5-4570 CPU (3.2GHz, burst to 3.6), and Windows 10 Pro. Also handy: 3 PCIe slots (one 16x and two 1x), DisplayPort, and USB 3 ports. And a serial port. Because business. It's also a vPro capable system, so it even has some rudimentary LOM stuff on board and ready to be an attack vector because Intel has problems with that. I'm going to drop a 240GB or so SSD in it (those run about $30 these days) and another 8GB RAM to.. bring it half to max - did I also mention it's got 4 RAM slots and supports up to 32GB RAM? No? Well, it does - and then basically leave it alone. The spinning disk in there hurts performance a good deal, as they always do, but it's a pretty decent machine otherwise, and it did for sure boot into an activated install of Windows 10 Pro. With shipping costs, this ran me a total of $105.
I like the way the Dell SFFs are done up - they just seem really solid and.. dense, really, which is nice - but I actually think I prefer the HP layout. It's a bit bigger than the Optiplex SFFs but all of the bays are on a swing-out bracket, and there was even spare mounting screws included (in a designated spot, from the factory) for adding additional drives. There's a 3.5" and a slim 5.25" external bay, and a 2.5" and 3.5" internal bay each. So, with some additional commodity mounting brackets, you could slot a total of 3 SSDs in here and have a pretty decent little storage server. Expandability is pretty nice on here - it of course uses low-profile cards, as do most any SFF-style machine, but three total slots is pretty good, and there's a good number of USB 3 ports on the front and back. (And, of course, vPro management stuff and the one somewhat neat thing that tends to get glossed over: the internal speaker's hooked to the sound card, so you have actual audio without having to hook up speakers. Not good audio, but not just the 1981-style PC beeper either.) One big drawback here, though, is that the power supply is totally nonstandard; sometimes these things will have an SFX or TFX power supply, which is at least pin-compatible with ATX, but in a weird size. This doesn't; the power going to the motherboard is totally weird. There's like 3 different, beefy 6-pin connectors that would be at home in an Amiga. It's a good PSU in there, but if it goes out, the machine is unlikely to be salvageable. Still, that's a lot of good machine and options for the $105.
Now, am I going to use this as a desktop PC? Of course not. It'll work fine for that purpose, but that's not really why I wanted to get one. I also got a 4-port GigE card (also HP, with an Intel chipset) that uses a PCIe x4 slot, and that's been added to it. In essence, this is going to become a router. Commodity WiFi routers cost about this same amount, but not ones that can be loaded down with Proxmox (and/or maybe Kubernetes) and pfSesne. (And obviously WiFi routers have WiFi, and this doesn't. But, I'm just going to keep using my cheap TP-Link router, and just make it not do routing anymore. It'll just have to manage WiFi and the what-passes-for-mesh networking I have.) So, for $100, another $30 or so for the NIC (you don't have to get a quad-port one, but they all run about the same price via the eBay) and about another $60 in some upgrades I don't really have to do, I'll have a pretty decent home router and edge server. And it'll be way easier to do WireGuard up to real cloud stuff too. And I can maybe finally use the IPv6 block I've had forever. And VLANs, because what every home network needs is 4 more networks laid on top of it!
In conclusion, if you need a decent amount of computing power, but don't have or don't want to spend a bunch of cash on a new build.. old business desktops are a thing to check out. $125ish for a machine that you can then slap an SSD and some sort of half-height video card into, and play some games or get some work done is a great deal - it's excessively hard to compete with that by building your own from scratch.