I installed the Teknonsha (I believe I paid less than $100 on line). I installed it exactly as Myle's article describes, with the exception of not attaching to the brake pedal. For this wire only, I just followed the second set of instructions and wired it to the LCM over in the passenger footwell (actually spliced it to the wire as directed).

To me it was difficult at all, just time consuming getting through the firewall and routing to the back of the X5.

If you buy the OEM hitch from BMW, the instructions reference where to make the connections, what part # you need and they mention a BMW tel # to call for a list of approved controllers.

In regards to your hitch, I had the same dilemma. BMW quoted me $1,500 for parts and installation. A local third party vendor quoted me $250 for a hitch including installation, but would not provide and install a wiring harness, as they had run into problems in the past. BMW do sell the wiring harness and modulator separately at around $200 (not installed).

The wiring harness is very easy to install but needs to be installed at the same time the hitch is (for easy access). I was also concerned that a custom mounting plate would also need to be installed to the hitch to hold the electrical receiver - another cost.

For $500, BMW provide a complete package, hitch and wiring harness. I went this route and it took about 4 hours. No drilling and very straight forward.