I looked into ready made NAS machines but wasn't sold on the software that came with them. Ended up building a small PC and installing OpenMediaVault on it which I have been super happy with.
Depending on how many HDD bays you need you can just buy a refurbished office Dell or HP and it'll do the job more than adequately.
He's also a thief of course, as that's the only way to become a billionaire.