The W140 car is very expensive to maintain and repair if you do not do the work yourself. I think that is one of the reasons why these cars are selling (relatively) inexpensively on the market today becuse a high percentage of owners of new S class cars do not do maintainance and repair work themselves. A 95 E320 at your mileage would be running around $18k. So you can see the S320 is not holding its value as well as the E class.
When I bought my 97 E320, the sale people were trying to push 95 or 96 S320 with similar mileage and price.
I do not mind payment $300-$400 to have an alternator replaced.
Well, a rebuilt Bosch alternator runs over $300 (list) for your car and that is parts alone.