39 Clues on a budget

If you've never read the best-selling 39 Clues series, I noticed a "buy one, get the next for half price" deal at my local Barnes and Noble. I don't know if the deals will get better or worse as we get closer to the April 5th release of Vespers Rising (the 11th 39 Clues book), but a series-wide 25% off isn't a bad price (particularly since there only seems to be one Complete Boxed Set left on Amazon).