> to pay someone to get you such a NAS and configure everything for you is still a fraction of cost, that you would pay for cloud providers.
Dropbox for Business costs what, $75/month for 5 users? That's less than you'd pay for an hour of a competent person's time.
I'm not a huge fan of Dropbox for several of the reasons that have already been mentioned above (I use SpiderOak myself), but on these specific points they definitely beat the roll-your-own approach.