Macbook vertical blue line

You have confirmed you have a hardware issue with the built-in Display Assembly since the line only appears in a photo of the laptop's screen, but not within a screenshot. If the laptop is still under warranty and does not show any signs of accidental damage, then Apple will repair it for free, otherwise you will need to pay for the repair.

Good job troubleshooting the problem.

Yes, unfortunately the complete Display Assembly will need to be replaced. The last Apple laptop where it was possible to remove the glass to access the LCD Panel was the non-Retina 2012 laptops, even then only by an unauthorized repair tech since Apple would only replace the complete Display Assembly. Unfortunately the design of the newer Display Assembly make it impossible to remove the internal panel anymore.

If the laptop is not under warranty, then expect to pay a lot for the repair (easily $500+ US, probably closer to $600 - $700 US as you mentioned in your original post). Unfortunately all of Apple's designs are like this these days....devices made up of only a few large replaceable components (Display Assembly, Logic Board, Top Case Assembly, plus just a handful of smaller components like an I/O Board for the USB-C ports).

You can always provide Apple with product feedback here (Apple won't respond):

Product Feedback - Apple

Or you can contact Apple corporate to let them know of your displeasure (Apple may respond):

Contact - How to Contact Us - Apple