First, I think some people are thinking of a different type of show. Most shows that are all or most kids, like the Christmas pageant, are generally still free. The OP is talking about a full production with stages, sets, months of rehearsals. Those usually have a fairly reasonable charge.
Second, my niece and nephews live two hours away. When we go down for their shows, sporting events, whatever, we always pay our own way. Sometimes, my BIL tries to pay but we feel that it our choice to be there because we love seeing the kids and it shouldn't cost them for our admissions.