ZFS doesn't really need huge amounts of RAM. Most of the memory usage people see is the Adaptive Replacement Cache (ARC), which will happily use as much memory as you throw at it, but will also shrink very quickly under memory pressure. ZFS really works fine with very little RAM (even less than the recommended 2GB), just with a smaller cache and thus lower performance. The only exception is if you enable deduplication, which will try to keep the entire Deduplication Table (DDT) in memory. But for most workloads, it doesn't make sense to enable that feature anyways.

That + full-disk encryption is why I went with BTRFS inside LUKS for my NAS.

They recommend 1GB RAM per 1TB storage for ZFS. Maybe they mean redundant storage, so even 2x16TB should use 16GB RAM? But it's painful enough building a NAS server when HDD prices have gone up so much lately.

The total price tag already feels like you're about to build another gaming PC rather than just a place to back up your machines and serve some videos. -_-

That said, you sure need to be educated on BTRFS to use it in fail scenarios like degraded mode. If ZFS has a better UX around that, maybe it's a better choice for most people.