It makes you wonder, though, if Hamas isn't just going by prior experience--"the Israelis value us so lightly and their own so highly that we have a reasonable chance of getting several hundred people released for their one, so we might as well start the bidding as high as possible". The fact that Israel is saying "Well, we can't give you these 450 people, but we can negotiate on the rest" seems to imply that Hamas is at least partially right.