2002 Mercedes Benz ML 320 Remote start

Hi My friend have a 2002 Mercedes Benz ML 320. She would  like to put a remote starter in it. So is this hard to put it on. I have put alot of remote starter in alot of cars, like Acura, Honda, Nissan, but i never put one into a Mercedes.  I went to Circut city, Best Buy, i asked them how much it going to be if i put a remote start into my friend Mercedes, and then they said they don't do for Mercedes. I have look into the wire diagram in this vehicle, i know it take some more work then a different one.  All is my question is how hard is that. Thanks for Help me FIrst