The thing is, I don't even know if you're paying Apple 100-200 bucks to replace the battery, or if you're paying them that much to replace the entire top case assembly, along with the battery, since it's so damn difficult to replace just the battery, I don't know if they even try. This is at least what they used to do.[1] I tried to research and find if this is still their practice but it was proving difficult. Very wasteful if so, and all likely just to make it difficult for the user to repair their own machine. (For what it's worth, recent MacBook Airs reportedly have Apple-replaceable batteries.)

[1] https://www.macrumors.com/2018/11/07/2018-macbook-air-batter...