Depending on how many disks you need, buying old PCs on eBay is the way to go because there are still some Xeon E3 ECC models available cheap ($100) with plenty

Depending on how many disks you need, buying old PCs on eBay is the way to go because there are still some Xeon E3 ECC models available cheap ($100) with plenty of RAM (16GB) and four SATA ports for a NAS.