Redmine

Hello there, I'm really new to redmine,
I'm playing with it for about couple of weeks, and was really surprised not to find any billing (for issues) plugin.
I looked through and nothing was found (except redminecrm surely). I'm almost 6 years ruby on rails developer and never paid for gems or libs I used.
I thought that ruby community is really open. I still think so.
That's why I'm asking where I'm wrong? Are there any plugin where you can just select some issues and right click to create bill from that?
Do anyone need for free?
I'm building it for myself https://github.com/IvanShamatov/simple_billing
It is not ready yet, but if you have any ideas or suggestions, I would be appreciate to here that.