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

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