Adorama Camera via eBay has the Synology DiskStation DS918+ 4-Bay NAS Enclosure for $569.03 + $21.96 shipping. When you add the , price is only $505.64.
Only a few available from this seller. Other sellers at similar prices are available, but don’t have experience with them like I do Adorama.
https://www.ebay.com/itm/Synology…2646
Amazon @ $549.99: https://www.amazon.com/Synology-b…B075N1Z9LT