Suppose Ruben decides to get the peach ice cream. Which result would be a cost?

 - Ruben will get to eat the peach ice cream. He likes this flavor more than strawberry cheesecake.
 - Ruben will give up the chance to get a free waffle cone. He would have enjoyed the waffle cone.
This result is a cost. It involves giving up or spending something that Ruben wants or needs:
Ruben will give up the chance to get a free waffle cone. He would have enjoyed the waffle cone.