Current NAS: FreeNAS with 6x2tb drives. Constantly 80% full despite constant cleanup and relocations/archiving.
So I came to own some of (free) WD RE4 2.0Tb Enterprise SATA drives. Drives are used, but not too much as these meant to last a very long time.
I already have 8 at home and 8 more to comes likely this week.
Long story short, after posting a question on expert forums here:
https://forums.servethehome.com/index.php?threads/need-help-to-decide-on-budget-storage-expansion.23695/#post-221447
Xyratex brand was mentioned and that sent me on a quite interesting chase. If you never heard about Xyratex brand, you're not alone. Neither had I. Quick research this company, now owned by Seagate, used to do OEM for Dell and Netapp storage for storage shelves.
So, this is what I got:
https://www.ebay.com/itm/Xyratex-JBOD-Expansion-Array-12-x-3-5-6Gb-s-SAS-Hard-Drive-Bay-HB-1235-Dell-HP/192823421241?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649
$105 offer accepted and $34 shipping (which was very reasonable - this thing is quite heavy and 24" long)
Also from eBay, I've added a SAS external card LSI 9200-8e and pair of SAS external cables. Total about $170
Installed it today and gosh darn, the whole setup couldn't be easier. I'll build new volume after I get additional drives but already could see new ones in FreeNAS.
Fine print gotchas: Did I mentioned it's 24" long and 19" wide? It also makes about 60dba of fan noise and has dual power supplies.