"Here’s why the cost of MIB3 soared: The time travel elements of Etan Cohen’s script had to be re-worked by Jeff Nathanson who needed more time to pull off the tricky plot device while Cohen worked on another project. So the film shut down for about six weeks, which is a rarity for a major tentpole, and then Cohen came back to finish the movie. That caused the cost to skyrocket from a range of $225M (which is what Sony claims as the budget) to $300M (which is what rival studios say it really was)."
http://www.deadline.com/2012/05/men-in-black-3-opens-to-1-3m-midnights/#more-277999