That seems quite hig to me. I just negotiated similar config. for my girlfriend's car except her's is a 335i and it only cost $636/mth with $3,600 out of pocket. I can't justify a $189 per month increase for a total of $6,800 over 3 years to go from an "i" to an "ix" just for 4 wheel traction/drive. Seems the dealership saw you coming. As an analyst, I visited and communicated with 5 dealers before hand and received esteimates ranging from $619-$760.
Try this link when calculating for your next purchase --
http://www.bloomberg.com/invest/calc.../leasebuy.html