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datahoarder
Who are we?
We are digital librarians. Among us are represented the various reasons to keep data -- legal requirements, competitive requirements, uncertainty of permanence of cloud services, distaste for transmitting your data externally (e.g. government or corporate espionage), cultural and familial archivists, internet collapse preppers, and people who do it themselves so they're sure it's done right. Everyone has their reasons for curating the data they have decided to keep (either forever or For A Damn Long Time). Along the way we have sought out like-minded individuals to exchange strategies, war stories, and cautionary tales of failures.
We are one. We are legion. And we're trying really hard not to forget.
-- 5-4-3-2-1-bang from this thread
Unfortunately I'm not familiar with the US market, but in Europe we have sites like Geizhals ("Skinflint" in the UK) that are excellent at listing electronics, so you could source them for cheap: internal drives, external drives
If whatever you end up doesn't have enough 3.5" slots, you can get these things on ebay to use them as a hacked together external housing:
You'd need to get the SATA cables out of your case though.
As for what drives to use: If you don't need redundancy/parity, then a single 12 (14, 16, 18, whatever you need) TB SATA drive will probably beat everything else pricewise. I'd say that leaves you with roughly $300 for the system itself, if you need to buy a new one.
Well, you only really need one or two drives. Are you sure it doesn't offer any SATA connections?
What about PCIe? You could use a cheap HBA card then.