If it's just the display, I think a replacement is about $300 from Apple.
Last time they replaced my display under warranty, they gave me a receipt with a breakdown of the components. The display would have been $350. That was on a 15" rMBP, so I can't imagine the 12" rMB to cost much more than that just for a screen.
But... those look like symptoms of a motherboard problem, which might actually cost $500 - $600, yeah...
Cross your fingers!