There was a talk recently Gabe gave a university, where he was sort of talk generically about how Valve compensates, and the figure of half a million was mentioned for a hypothetical hire from Weta. That's the closest to a number from Valve I've heard.

Edit: found the talk and the moment, and it wasn't quite as I remember http://www.youtube.com/watch?feature=player_embedded&v=t... Rather he was talking generically about employees getting paid something that reflects the value they bring.