Hi, I am considering buying a BMW X6 and wanted to know an approximate cost of the maintenace for such a vehicle...?

If you are purchasing it new (which I'm assuming you are, since the car just came out) the maintenance will be free for the first 4 years or 48,000 miles. It's part of BMW's full maintenance program included on all new vehicles

deauto is right...except it is for 4 years or 50,000 miles, whichever comes first and it even includes wear and tear items like brakes, air filters, etc.
After this time, though, it will be very expensive to maintain.

Make sure you don't forget about insurance. A BMW can be expensive to insure, depending on your driving record.