Suppose Owen decides to plant the daffodils. Which result would be a cost?

 - He will save some space. The daffodils will use up less space than the elm tree would have used up.
 - Owen will give up the chance to look at the elm tree. He thinks it would have looked more beautiful than the daffodils.
This result is a cost. It involves giving up or spending something that Owen wants or needs:
Owen will give up the chance to look at the elm tree. He thinks it would have looked more beautiful than the daffodils.