StroemPhi
commented
3 years ago 
There are different kind of fees involved in the organization of academic events, such as member fee, reduced fee, early bird fee, box office fee, or gold, silver and bronze sponsor fees. As of now the destinction of what is really common practice is not so clear. Thus it seems best to only have the two classes 'attendance fee specification' & 'sponsor fee specification' for now. To indicate the more fine grained kind of attendance fee specification a user can use the rdfs:label on an instance of this class.
We might add more subclasses, once we have a large enough data set from which these can be derived.
The fee of an academic event can be understood as a iao:'condition specification' that specifies how much money has to be paid in order to be allowed to attend the event or how much money has to be paid to be an official sponsor of the event. It is a condition which is part of the academic event type specification that gets realized by the event. The event fee specification must be represented by a literal value of the amount of money that has to be paid and a symbol that indicates the currency that has to be used for the payment.