Buildapc

First, join [email protected].

Next, you can build an APU-only build with some pretty small ITX cases that basically can only fit an ITX motherboard and a flex PSU. You'll have all the capabilities of modern CPUs and 1-2 slots for m.2 drives. Unfortunately, ITX builds can be expensive, depending on what you buy, and your part options are more limited. If you can wait until Christmas, computer parts typically have their best sales around then (not Cyber Monday).

If you don't care about future upgradeability, there's some interesting mini PCs I've seen that sometimes have replaceable hard drives and/or RAM, and they can be a little cheaper. I don't remember any specifics, but they're out there.