I don't think there's really even a rule of thumb about that these days. It depends on so many thing. Ladies have traditionally most sought after than the other disciplines (probably all of them combined). An American lady would probably make more. There's Kwan, who doesn't even need an OGM to rake in the money, but her endorsement money won't be going to the OGM.
Then there's the popularity of the sport. No one will be making the money the skaters of the 90's made for a while. IMO, 1 or 2 skaters may make that much, but most will have to settle for considerably less.