Maybe there is an alternative to a dedicated NAS via a syncthing machine?

Doesn't rely on cloud

Can share data with family members, no cloud sync needed

IP cameras recording locally is not clear whether it's to a UNC path or to local on device storage. I'm gonna take it as recording over lan to UNC path and say yeah syncthing isn't the best for this but it could sync that path elsewhere.

This is what I do, heterogeneous synced storage through Resilio (but could have chosen Syncthing). One of my servers is even a phone (cracked screen).

I have roughly the same requirements. For me it worked out more time and cost efficient to just leave the PC on. Logistics, management and maintenance were a pain when I had a NAS.

I just split the difference and built my NAS PC with power efficiency in mind. Big fan of the ECC-supporting C3xxx Atoms. I have an eight-core version (which is total overkill here, even) in my NAS with ECC DDR4 and a 8x8TB RAID-Z2: https://www.supermicro.com/en/products/motherboard/A2SDi-8C+...

I'm using a Xeon-D machine, quad cores, with ECC DDR. It's overkill for just storage, but I also run a bunch of VMs on it. It's my router (pfsense), my storage box (samba w/ZFS on SSD array), my ssh utility knife, my "run vendor crapware" (e.g. Lutron's RadioRa software) Windows box, etc. QEMU is fantastic.

My home's IT power draw is about 45 watts, using two access points, that server, and a bunch of little widgets (e.g., Rainforest power monitor, Lutron bridges, etc).

That will go up when I add a big switch, but it's not bad for the utility I get.

The thing is, if you don't want to loose a lot of performance on that storage, either a bought or a built NAS will set you back 1000+ bucks; you can run an idling desktop PC for at least 5 years for that price (80 W idle power consumption, 30 ct/kWh electricity cost).

There are more dimensions to my decision than the raw cost. I sit next to it and enjoy it being relatively silent.

My PC is almost 100% silent.

Did you manage to do that with hard drives?

No which was part of the original point.

Management is a pain? I have a Synology NAS, and in 8 years I can't remember anything I had to do to it beyong initial setup and port-forwarding. You could argue they are underpowered, not cost efficient, or whatever, but technically I had less issues with it than I did with OneDrive.