Note sure about that. I've been tinkering with computers for decades now and I don't find it rewarding (anymore) to fiddle around with low-level stuff. Did this in the past and had fun doing it as a hobby, but by now I'd consider it a waste of my rare spare time to setup a tool that I could purchase pre-built. One of the reasons why I considered building myself a FreeNAS, but did away with the idea pretty quickly.
Even more so, if you're making money off using computer hardware (OP sounds to be a professional photo-/videographer) your time is far too expensive to invest it into financially "unproductive" work like setting up some computer/FreeNAS system.
Don't get me wrong - if you're rewarded by this kind of work that's great! It's just not for everyone.
Umm - not sure if I can follow you on the last sentence. But the cost for the drives is the same for both a NAS box and a FreeNAS approach, so they're out of the equation.
Thus it's
- three to four hundred dollars for a plug-and-play NAS box
- vs. two to three hundred (optimistically calculated, probably rather four hundred as well) for a FreeNAS-suitable hardware _plus_ the time to understand it, gather the components, put it together, set it up, test and maintain it
- (vs. four to five hundred dollars for a Mac mini plus higher costs for external drives vs. the internal ones for a NAS box).
And I didn't even factor in the higher electricity cost for a universal-PC-based FreeNAS vs a dedicated NAS box, both running 24/7.
Granted - the lower range boxes have no expandability, but you can put up to 12TB into a 2-bay-box like the 213air already. With e.g. the 2-bay Synology 713 you can later on add an expansion box with another 5 bays. Or you simply purchase another "small" box, plug it in and are ready to go.
And if you want to go _really_ big you can go for the Synology 15xx series (the even bigger 18xx and 24xx series are overkill for SoHo use), which allows for two expansion boxes, providing a total of 15 bays - that's up to 90TB of storage...

I'm not aware of any PC housing coming even close to offering that many bays...
Definitely faster and less hassle compared to changing and adjusting a complex PC-based NAS imho (maybe I'm just not techie enough, anymore - but I guess so is the OP).
That is only if you don't factor in the time you need to work yourself into the necessary knowledge levels and the time required until all is configured, set up and running.