Yeah the standard flat rate fee for motherboard related issues from Apple is just about $300. With this in mind it's usually a better idea to take them to Apple then use third party shops. I've had the exact same issue happen to me on Apple laptops all the way back to my 2008 Macbook Pro and eventually Apple made the same extension for that model as they are with these newer models. After a few years the video chipset seems to have connection issues that may or may not be solved with a reflow attempt (baking the logic board in the oven)