Both the Halo 4 Crimson Map Pack and Majestic Map Pack -- originally 800 Microsoft Points -- are now available for 600 Microsoft Points. However, if you add in the recently released Castle Map Pack -- 800 Microsoft Points -- it becomes a better deal if you just buy the War Games Map Pass which is also discounted by 400 Microsoft Points; it's now 1600 MSP as opposed to the original 2000 MSP.
Basically, if you only need one add-on, purchase them individually. If you plan on getting all of the downloadable content, buy the season pass. You can make your decision once you get to the Xbox LIVE Marketplace. Microsoft has not said how long the sale will last.