Aha, the trick to this, I have discovered, is to get a crappy 48-port switch that nobody wants off eBay. Something like an HPE one, you know - the kind of thing that hangs around on eBay for months then goes to recycling. They're in decent cases and the 48 ports means they already have a huge hole in the front that's a really handy size for stuff.
I got this one for a tenner: I didn't want the switch, but I got a 1U rack case, a 12/5V dual PSU and 14 decent heatsinks for that tenner, which counts as a bargain as far as I'm concerned. This is hugely better value than getting a new 1U project case, which will be more expensive, not have a big hole in the front, and will probably (IME) be worse quality.
They also tend to have LEDs and management ports that can be repurposed for fun. That's the plan here.