First, thank you for posting this as a reminder to those who might come along in the future and benefit from your experience.
Second, I've been fined for a violation when on vacation, and understand it's no fun.
However, whether I agree or not with your statement that the fine is excessive is irrelevant. I am not an Austrian citizen--this is their law and their prescribed punishment, so what I think about it makes no difference. And I have never understood the "I'm a tourist, I should not be penalized" idea...why? Sure, it would be nice not to be penalized, but then any non-native could use this as an excuse, rightly or wrongly. I am not saying that in this instance you were trying to get away with anything, but the police have no way of knowing this.
And, I do hope you are able to put this behind you and enjoy the rest of your trip.