Should the money be returned to the person who broke the laptop's button and paid the full price of the keyboard, knowing that there is another shop that can repair the button at a lower cost?

If a person damages something while performing an action they are unfamiliar with, they are only liable for the value of what they damaged. If they give you more than that value willingly, it is permissible for you to take it, and you are not required to return the excess.