When you pay the annual fee of $129 to join PMI, and then decide to apply for the PMP exam, instead of paying $555 to take the PMP exam, you will only pay $405. That is a good amount of money saved!
Another related piece of information, the annual renewal fee is $119. It is $129 for new members.
Visit the following PMI website for more information on membership: http://www.pmi.org/membership