Good price right now (still too close to Chia mania sucking HDD prices higher) 1.2 TB HGST SAS for 50 a piece, but will run you still 400 for 8 and space will be - depending on raid-level - only 7 or 8 TB. Any particular reason why SAS?
If "mostly space", switch to 3.5" and 8+ TB SATA disks. Maybe lookup "wd book shucking" with articles from Reddit and videos on Youtube. 8 TB WD Book for 160 right now (all prices EUR). Quality will be quite good, those are usually WD or HGST overproduction enterprise drives at 7200rpm. Keep enclosures for warranty return should you need it and be prepared to mod power supply of disks in case drive reacts to 3V3 pin. Like this: Solutions: Shucked WD 8TB Easystore 3.3v PIN Issue I got some braided PSU cables, opened backside of connector and ripped out the 3V3 lead completely. HDDs only need 5V and 12V. Beware of Molex to SATA connectors that can catch fire. If this isn't a ready made NAS you already have I recommend to google that as well.