Welcome to the forum.
The article/survey available at the following link is from 2005-2006 but nonetheless might be helpful.http://www.writersmarket.com/assets/pdf ... Charge.pdf
I work as a freelance editor rather than a writer, but from the beginning I charged (although less than I did after I became more experienced). I felt that since the client was benefiting from my work, I deserved compensation in return. But if the client weren't benefiting, it would suggest I wasn't yet fit to offer my services, even for free.