I’ve got a retired server from our now closed office. This unit is not suitable for a quiet office environment since it has lots of fans.
As a complete working Win10 system (120+120+2*30+4*20+2*30+40=480) = $400 ($360 w/o license)
CSE-823TQ-650LPB - Supermicro 2U rackmount chassis, 650W supply, six hot-swap SAS/SATA 3.5” drives, CDRom
X9RD3-F-B - Supermicro dual Xeon, hardware RAID, SAS/SATA – was running Server 2008R2 but now Windows 10, 32GB memory
Windows license
Four ST3300657SS - SAS 15K 300GB drives, were RAID01, now un-RAID
Two ST3450857SS - SAS 15K 450GB drives, were RAID1, now un-RAID
Two XEON E5-2609 with heatsinks/fans
* System will run Windows 11 with installation tweaks (no TPM-2.0), Windows Server 2012 (maybe Server 2016?). Do a Google search for motherboard.