Personal anecdote: I have had an old Synology DS215j using WD Blues for about eight years now, and the SMART checks show the drives are within spec.

First, I'd go with making sure you have 3-2-1 protection. It is better to have RAID 1 with two Blues than one enterprise drive. If you already have 3-2-1 protection in place, then move to higher tier drives.

Focus on the backups and getting that in place first. Ideally, CMR Reds are what you should be using, but if money is tight, blues can work.

The cheapest solution would likely be a Mediasonic Probox or some other USB drive, throw some 20 to 22 TB drives in that, and call it done. The ideal solution would be to have a four bay NAS with RAID 5 or (even better) RAID 10, so you can keep snapshots, the NAS can optionally do backups, etc.

Terabox only allows 20 files to be saved on the free plan. Each file can be a max of 4 GB, which means that you can only store at most ~80 gigs. That is the main gotcha.

The absolute cheapest way to get storage. For the barest bones, ugliest setup, I've seen people have two PC power supplies on their desk, a motherboard, a few SATA cards, and a number of drives plugged into the SATA cards, and using Linux + ZFS + Samba for the heavy lifting. Alternatively, a "NAS PC case" with a decent motherboard and such should work.

If I were building the cheapest way to have a lot of storage, but have a warranty, I'd go for a higher end QNAP NAS that supports QuTS Hero, even QES. I would then load TrueNAS SCALE on the QNAP hardware, use ZFS from there on out. This ensures a lower attack surface, and ZFS without any added stuff. The QNAP hardware isn't cheap, but it is fairly reliable.

I have had APFS + encryption fail me once, where I wound up losing all data on the drive completely. It was just a copy of data so it wasn't a major loss, but it was something that concerned me.

As others have said, the simplest way is to just use APFS + encryption, copy the files, call it done.

However, what I do is format the external drive with ExFAT, and use Borg Backup with encryption. This ensures that I can pull the data off the drive, regardless of the data being on a Mac, Windows (with WSL2), or Linux. Borg Backup is an open source utility, and has a lot of presence, so it won't be going away anytime soon. The nice thing about Borg Backup is its deduplication, so if you back up a folder twice, the space used will be minimal.

Another idea is to use Cryptomator. This works on Linux, Mac, and Windows, and you create a vault (which is a folder with encrypted contents), mount that, and from there, copy your files into that. The nice thing about this method is that it works on all platforms (assuming you used ExFAT for the filesystem), and provides solid security.

If just Mac-only, the simplest will be using encryption with APFS, but making sure you have multiple copies on multiple drives, just in case.