Suppose Lucy decides to join the Photography Club. Which result would be a cost?

 - Lucy will save some time. She would have spent more time in the Theater Club than in the Photography Club.
 - Lucy will give up the chance to be in the Theater Club. She would have had more fun in the Theater Club than in the Photography Club.
This result is a cost. It involves giving up or spending something that Lucy wants or needs:
Lucy will give up the chance to be in the Theater Club. She would have had more fun in the Theater Club than in the Photography Club.