Difficulty/Cost to repair drywall from tv mount?
If you have the willingness, then you can do it yourself. And, you'll get experience to use in the future.

Well I started describing what you need to do, but it was getting too long. And, I realized that you can find lots of video on this if you Google "drywall repair". So I think your best bet is to do that. Seeing it done is a lot more informative that reading about doing it.