I would recommend that you save the money for more books and spent it later on exam simulators.
Again with the Agile PrepCast and Mike's book you have enough knowledge because they are written
to save your time in a way that you don't have to read all PMI recommended books which are listed here:
www.pmi.org/Certification/~/media/Files/...nsightsAIGLE418.ashx
Training for Project Management Professional (PMP)®, PMI Agile Certified Practitioner (PMI-ACP)®, and Certified Associate in Project Management (CAPM)®