Suppose Brendan decides to plant the magnolia tree. Which result would be a cost?

 - The magnolia tree will use up more space than the lilies would have used up.
 - Brendan will get to look at the magnolia tree. He thinks it will look more beautiful than the lilies would have looked.
This result is a cost. It involves giving up or spending something that Brendan wants or needs:
The magnolia tree will use up more space than the lilies would have used up.