I'm having mine installed at the dealer. I'm waiting for an email with the cost. I'll post the info when I get it. From my research, the BMW hitch installs somewhat differently from aftermarket hitches in that it has some additional supports. Also, my dealer gave me a mini lecture about the fact that any kind of electrical work done on the car by anyone but BMW would "void" the warranty. I know that is highly debatable, and I'm not trying to start any kind of discussion about that point, but I'm just going to go with them for installation. That way I won't have any kind of problems or liability later. According to BMW's printed instructions for the hitch install, it takes 2.5 hours. So that is what I expect them to charge.

You won't need one for your application, but there's another thread discussing brake controllers. It has a link to the instructions for the hitch installation.