Well I guess asking money for an open source product isn't a custom. It's written in Python, right? So the end product is the source code as Python is interpreted. It would be very, very easy to just get the code and change it or share it freely anyway.
There's not really any point in asking money for it, although donations are of course always usefull.

In my opinion, asking money for it is a bit weird. Donations are a better and less intrusive way.