My friend's E38 was used for commuting around 100 miles daily, interstate mostly plus long trips on weekends. I serviced that car, and in 2 years, he put on it around 55K miles. Only things he serviced were brake pads, filters & spark plugs. After this period the car was due for front shocks & control arms. That's it. If you commute on interstate, you should not need a lots of money for maintenance. But this depends on your buy...
JOY = BMW