If your referring to mine, aftermarket - Hidden Hitch/Drawtight model with the tow ready circuit isolating wiring kit - total was $260 and 4 hours of my time - looks better than the BMW and works great.

I just pull a small trailer, but if I was pulling something a bit bigger, I would have done the BMW harness which is pre-wired, so a 2 minute install and then have the car programmed so that you get the stability control programming for the trailer, but I would still use the same hitch as it works and looks better than the OEM one. Price would end up being the same approx if you did this hitch and bmw wiring and programming.