Searching eBay for (1U server) produces roughly 2500 (USA) results.
Searching for (2u server) produces roughly 3000 (USA) results. Many of the
results are for multiple items sales (a batch of used servers).

I get the impression (and hope) that many of the PCIe riser cards are just
right angle adapters.




--

I wrote:

This is just fascinating me. Apparently only for people who can build
stuff. That's what I was looking for. Otherwise, everybody would be
doing it.

https://youtu.be/epIlB49SNTI?t=474

There he is self-critical about his system, but if you zoom in and look
at the specs, you will notice it's running at 2.5 GHz. There are cheap
Xeon CPUs available running much faster than that.

This is thrilling... But must avoid the pitfalls. Lots of research
ahead. Wish I could do it with my Q9550s. But it looks like basically
the same thing, except having to buy them again.