ALL Linux distros are free, BUT most of the computer magazines charge a small value for the physical support. I would say your work fall into the same cat, the base lib may be free, but you are exposing it to a world it was not exposed before, so I recon it's up to you to decide if your time and work should be rewarded.
another example, Linux is free but if you take your pc to a techshop, they will charge for the installation of it onto your computer.