If you don’t want to use it as a “server” so you can run things like Plex, you could just get a “DAS” instead.
DAS=direct attached storage
NAS=network attached storage
A DAS is kind of just a “dumb” box. You plug hard drives into it, connect to your PC, and it’s detected as external storage.
A NAS is a computer. It has a CPU, memory, maybe some flash storage for the OS, etc.
If you don’t need that extra functionality for running a server, then it’s not really worth paying $1,200-$2,000 for a NAS IMO. It would be kind of like buying a Macbook Pro to use as an external HDD.
Even if you got a DAS that supports “RAID” (redundant array of independent disks):
Most will probably be cheaper than a NAS.
In terms of costs, it would probably be:
DAS (Non-RAID): $100-300
DAS (RAID): $200-400
Entry-level NAS, 4-bay: $300-600
Those are just guesses, prices vary widely depending on what exact features you need.
Beyond that it’s hard to gauge how much you’d want to/need to spend without knowing the exact things you want to do with the NAS and the exact features you expect.
But if all you need is essentially just a multi-bay hard drive “enclosure”, a NAS really isn’t worth the extra money.
Try reading some reviews/doing some comparison on a site like NewEgg for “DAS”:
https://www.newegg.com/p/pl?N=100008040%20600535778%20600535780%20600553213%20601276191%20601276194%20601276195&Order=BESTMATCH
versus “NAS”:
https://www.newegg.com/p/pl?N=100161337%20600016039%20600016040%20600016043%20600016046%20600418375%20600418376%20600418381%20600521581%20601296264%20601296266&Order=BESTMATCH
And you can get an idea of just how drastically it varies.
So, that being said… is all you want to use it for is a hard drive enclosure? Do you need RAID? Do you have any plans for it besides just plugging it into one PC?