I think you could do this with open source, but it would only last so long. I tried this a few years ago (I found some open source software, fixed bugs and added some features) and sold it.

In the beginning I got sales. But over time, I got less and less because people would just re-package it and give it out for free (they are allowed to do this under the GNU).

I suppose it depends on your demographic of users too. More tech savvy users will figure this out quickly