Your setup isn't a bad solution. It's pretty good and to be honest it's exactly what I've considered setting up with one of my technically literate friends.
The catch is, this solution only works well for an IT geek who can do it themselves. It doesn't work for the vast majority of people out there. Google would. An enterprise cloud-based solution also has a few less weak points compared to a homegrown one like this.
In summary, when you factor in time, ease of maintenance, and increased risk of failure, however slight it may be, the cost effectiveness of a Google Drive solution at the rates listed in this article holds it's own in my opinion.