Is GOES a free addon for Nexus/Sentri Users? If this is the case, it begs to ask why Goes cost me $100 and then Nexus cost me another $50.
The extra $50 is for Canadian approval. If you have the Nexus/sentry cards, you already have US security approval - thus no fee needed as GOES is purely US.
The following is NOT the reason per US border:
As has been said before many times, GOES is not an add-on to anything. GOES is not a trusted traveler program. GOES is simply a web application system used for applying for various trusted traveler programs, including GlobalEntry, NEXUS, SENTRI, and FAST.