I can't recall the exact amount, but I think I paid about £45 for a ticket to see Patrick Stewart in Macbeth in the London West End a couple of years back. Currency convertor tells me this is about US$71 or AUS$78. Looking at how much your son paid for his tickets, Miss N Thrope, I can't see myself paying that much!
Not only did he pay for the tickets but he has spent nearly $400 for ihis return airline ticket to Brisbane. However he will be staying with his best friend (who moved to Brisbane about 4 years ago). They have been friends since they were children. It will be my son's second trip to Brisbane - he previously travelled there to be best man at his friend's wedding.