Yeah, depends how long ago the seller bought them... Back in the day, they could have costed that much... At the time when the seller bought them...
That's correct, 450HP is the max output according to the turbo chart but I wouldn't pump that much with ceramic turbines.
Yes, R34 M-Spec turbo's are just ceramic internals.
Could just be bad lighting in the photos, but they don't look brand new to me...
And to be honest, I would not bother spending $500 on stock R34 GTR turbo's, just buy new -7's.