I could really use some help from current freelancers on what their average rates are for their work. I am leaving my ad agency job, where one of my primary duties was copywriting. They really like my work and would like to use me as a freelancer for some of their projects, especially for clients who have commented positively on my writing.

I haven't worked as a freelancer before - I've always been an employee.

What is a reasonable going rate that won't get me shot down, but isn't shortselling my work, either? And is it better to be paid per project or hourly? And does the answer to that question depend on the length of the piece?

Any advice would be very helpful...I thank you!

wow   , good  luck and congratulations.   I 'm  sorry I don't have  any advice for you. 

Freelance usually gets paid per project.  As for rates, sorry can't help you on that. The one person I asked, is a long time freelancer and has higher rates. BUT she did say that the length of the article can also raise the price paid and some will pay per line.

Maybe you can ask where you work at the moment what they pay for freelancers..

Hope this helps (it did for me): link

eta: I've also found the advice on The Renegade Writer to be useful