FWIW, personally I find it hard to argue for an ECC fileserver when files are created and edited on non-ECC clients. Since the server’s pretty much just a transport layer its file data DRAM residency time’s typically short compared to client side. So in order of increasing cost and diminishing returns it probably makes most sense to DDR5 the clients, DDR5 the server, EC4 the clients, and then EC4 or EC8 the server.
I can still get KSM32ED8/32HC and MTA18ASF4G72AZ-3G2R no problem. US$ ~5.00/GB before tax when non-ECC DDR5 M-die’s closer to US$ ~3.33/GB, though.