Good work! If you really want to save every possible penny, you could make the trip for $2.50 each way:

Inbound, take the #62 public bus (which follows about the same route as the express bus but makes more stops) for $1. Then take the PATH train (instead of NJ Transit) for $1.50 (just raised from $1 on March 25). PATH goes direct to the World Trade Center, or you can change at Journal Square to go as far as 33rd Street and 6th Avenue, near Penn Station in Manhattan. You can do the reverse going outbound.

This alternative takes about twice as long, so don't do it if you are rushed. Saving a few dollars is not worth missing your plane, obviously.

Bruce