I've been keeping LR4 stashed in my Amazon cart for weeks now to keep track of its price and it recently dropped to $100! Anyone looking to buy should probably do it soon, I'm guessing it's for Black Friday.
I saw it for $80 this morning on, I believe, NewEgg. Amazon is going to have it as a lightning deal in about an hour and a half. I predict they will have it for 70 or 80 bucks but that's for a very limited time.