> What about the storage devices (the S in NAS)?
I have two SSDs on it that are powered by the RPi itself, so the whole package is < 18W. Also, SSDs use way less power than HDDs.
> Which would be 13 kWh per month. If we're comparing to monthly fees for cloud storage, it's important to look at the same time frame.
Yes, running at max load. A more realistic load will be 3W/hr -> 72W/day -> 2kWh/month. That would put it at ~0.3€/month at a realistic load and ~1€/month at max load (0.15€/kWh where I live).
You also have to take into account there's other stuff running on such "NASes", like the PiHole, a git server, a plex server, which are going to cost you separately if you need them. On the other hand, my setup cost me ~300€ (RPi, charger, drives, USB-SATA adapters), which buys a whole lot of VPS and a whole lot of online storage.