I have been asked to quote an hourly rate for freelance programming for a Rails project. Although it would be my first paid project on Rails, I know the technology well from personal projects and have a decade of professional programming experience. This would be my first freelance project ever, so I have no idea how to find out what the going rate for my services should be. Obviously, if I quote a rate that is too high, they may choose someone else - too low and I may feel cheated later on. Any suggestions?

Update: I am in NYC and the project is scheduled for 6 months to a year (but this seems unrealistic - I think it will be a multi-year project). I would develop on site (at a corporate location) with one other developer and the project would consist of about 200 custom-built pages initially. 10 hour days with weekends and additional overtime as required. The customer has given no information about how much they will pay - "a competitive rate" - they want me to start the discussion.