When I build my NAS/server last year, I bought a used Dell Optiplex from 2013 on eBay for $50. I tossed in an old SSD I had laying around, and squeezed in 42 TB worth of HDD drives. I added a PCIE SATA expansion card, and a 10 gig network card for 60 bucks to improve performance.

The only real downsides of doing it this way are

• No realistic way of upgrading hardware
• Limited space for internal drives
• No hardware transcoding abilities out of the box
• More power consumption than buying something newer

I use Kopia to backup to Backblaze B2. I also use the Kopia UI since I can’t be bothered to figure out the cli for it. I have it running constantly in the background so it automatically takes care of everything.