I really dont know the answer but have heard figures from $16-$40/hr
...not many get the pointy end and typically they have to create a lot of business to get the big bucks.
Are you asking the question to know what to ask for in a new job?
Full time, part time, casual will also make a big difference to the cafe owner. Paying you top dollar in the quiter parts of the day can be hard to justify.
If you are "that good" then why not see if you can work on a unit price. I dont know if its legal but a set figure of say 70c a cup might be a win-win for both the owner and the barista in a busy cafe as long as you were happy to work for $60hr when you were getting pumped and then work a few hours at $7hr when it was quiet.
Of course this is the math that the owner is doing to justify a full time wage anyway.