It's expensive to do things properly.
I figured awhile back that to do ZFS properly you'd want to do raid-z2 with at least 6 drives, and assuming you buy proper datacenter drives, a 12TB WD Ultrastar drive will cost you
$615 per drive, and multiply that by 6 drives you're already $3690 deep before you even buy any other parts of your NAS.
https://wintelguy.com/zfs-calc.pl
Don't forget about backing up your NAS if you're going to store data that you don't want to lose on it. If you copy paste your NAS so you can replicate your NAS across those 2 devices you basically just doubled your cost again.
Edit: You can shuck drives too, and current going price is
~$350 for 14TB. But it's still $2100 before you even buy the parts for your NAS.