It seems like it would be silly to buy 1 and 3 without buying 2, even if it isn't on sale. So for anyone who is wondering, you can buy book 2 here [amzn.com]
for $22.98 bringing your total to $55.90 (+tax in certain states) for the entire set.
Edit: Plus reps to DealHo for the very useful information about books that continue the story. Thanks!