From the announcement:
For a limited time, DrivethruRPG and Troll Lord Games have set up this amazing MegaBundle of items featuring Castles & Crusades! From the Players Handbook to settings to supplements to adventures, this one covers them all! Get $150 of books for less than $30! A great chance to get the ones you are missing or get started with a new game that is easy, fast, and fun to play!