The most cost effective approach would be to use the Cisco Press CCNA Security IINSv2 640-554 Official Cert Guide, which is written by Keith Barker and Scott Morris (I admit, I am a little bias towards this book).
The Cisco Press 640-554 Official Cert Guide is streamlined and focuses on preparing a learner by explaining and demonstrating all the topics listed on the blueprint for the 640-554 exam. That blueprint can be seen on Cisco’s site by following this link. A account (free to set up and use) is required for access to the blue print.
Another training option would be to take the full IINSv2 course, offered by a Cisco authorized learning partner, where you would have access to the official course material and labs for your studies.
Regardless of which content you use to study and prepare, an excellent free resource is the Cisco Learning Network, which has discussion groups and lots of people ready to jump in to answer questions regarding technologies and topics centered around Cisco certification and the associated technologies. The link for the Cisco Learning Network (CLN) is here.