The cost to ATC and the airlines probably outweighs the cost fines and court costs given to the three offenders. Pilots and the atc controller all had to take time off as well as taking up the time of a Dr to treat them or pass them fit and assuming that the airlines had to re roster other pilots then the final cost must have been quite high. So a jape has cost some people some serious money even ignoring the serious possibility that an aeroplane could have crashed as a result of three peoples stupidity.