MacBook Pro Dented - Cost to Fix?

You may get a sense of cost here:

https://support.apple.com/mac/repair/service

AppleCare+ will help off set the expense of accidental damage:

If you have AppleCare+ it will cover a large portion of accidental damage.

https://www.apple.com/support/products/mac.html

AppleCare+ (similar for iPhone and iPad, each incident of accidental damage) for Mac will carry its own price tag. Screen damage or “external enclosure damage” will run $99 per incident, while other damage, including water damage, will run $299. Users receive coverage of two incidents under AppleCare+, and after the two incidents have been used up, out-of-warratny replacement rates will apply

Bring it in to any Apple Store for a free evaluation and estimate.