Not really...they've been $80 - $100 for some time. If there's any reason right now, it's because the Cavs haven't gelled and look horrible as they work out some bad habits.
Let's face it, rookie cards are generally valued based on what a player may accomplish. And in Lebron's case, what else does he have left to accomplish?
Seems like most modern cardboard has cooled except the newest rookies. There is still demand but over saturation and a new batch of up and coming young stars have cooled off many of the older rookies.