Why not just start going on interviews? If you really are that good, you will get offers and can see how much you will be able to make.
What city?
Github, heroku, twitter, any major ruby shop consider to be big pay pretty salary. I think these guys pay minimally 90k USD. Just look at glassdoor.
I'm looking for companies that pay very well for Ruby dev's
The answer you're looking for depends on two key factors:
1. What part of the world you want answers from.
2. What you consider to be "very well' paid.