I'm uncertain of why $40 vs $300 is even a point of debate on HN. The latter is a one-time investment and you likely can expand it a bit i.e. add a 2.5" or M.2 drive later.

What's the gain of running 12 RPi, exactly? Do you do research work requiring distributed low-cost computing?

I do distributed computing, and doing it at home for low costs without cloud spend helps…

Are virtual machines not an option for your use case? From the outside looking in they appear like they would be easier to manage and far less costly.

They are if the GPU can be attached. I avoid virtual machines in favor of container workloads from containerd for this reason. It’s easier to attach Mali GPU and do my work than it is to find cash in this economy for a dozen RTX’s.

A “server” doesn’t need to mean a pizza box with 15k rpm jet engine fans.

My server is repurposed desktop hardware in a desktop tower case and is nearly silent except for the subtle hard drive noises. The hardware cost next to nothing and is far faster and more capable than any pi (except the pio of course which wouldn’t be used anyway).

An ITX isn’t the competitor for a Pi. I’d suggest a USFF prebuilt. I use an HP Elitedesk and Dell and Lenovo each have similar tiny PCs. They’re nearly silent or completely silent, and half the size of a Mac Mini. Cost is about $150 for hardware that is more than enough for me, plus they can have 1-2 SSDs and a hard drive inside the case.

Clarification: They're about half the height of the OLD Mac Mini. Better comparison: They're the size of a typical hardcover book if you chopped it to be square.

You’re running the pi and drives in a plastic take away container off usb power for that price.

At the very least you want the case and psu. At which point the question is which cpu+motherboard+ram combo do you want in that case. The rpi is one of many such options and is actually quite expensive for the amount of cpu+ram you get for the price.

Does that $40 include everything to make the Pi work?

After looking at lots of small board options, I got a NUC for $110 to be the brains of my NAS.