Well, I can answer your question. I agree that the dealer may not be the best place to get one put on, but I negotiated one as part of the deal with my dealer, so I got it for 'free'. The price they took off the amount of the car was for the trailer hitch with the wiring harness connector. The cost I would have paid was $500 for that, installed. There is another version that is just the hitch and no wiring harness, which is like $400 or something.
You should know that adding a trailer hitch is not equivalent to what you get when you order the trailering package from the factory. That contains a HD oil cooler, among other things for added towing capacity. So the actual towing capacity of the traverse will be less with an aftermarket hitch only.
I only needed mine for my bike rack which attaches to the hitch...so the towing capacity was not an issue.
Thanks,
Joe