Final answer:
According to Medea, the cost of her grief is betrayal by her husband, Jason.
Step-by-step explanation:
The cost of Medea's grief, according to the text, is betrayal. In the play, Medea's husband, Jason, leaves her for another woman, which causes her immense pain and grief. She feels betrayed by his actions and seeks revenge as a result. While love, revenge, and loss are all present in the play, it is ultimately Jason's betrayal that inflicts the most grief on Medea.