For what it is worth...

I was recently asked the same question by a friend. She was looking at a diesel.

The short answer: If you are looking for an E-class around 1997 to 2002 a low end six will go for about $5,000. I think we all know that even a low end Mercedes is still quite nice to drive, but you will not get a 4-matic at that price.

A diesel from that time frame booked out at about $3,000 more. Now getting 36 mpg is better than getting 23 mpg, but how many miles will it take to break even on that $3,000 bump?

A gas car works for me since I don't make that many 700 mile trips anymore. The range of the last diesel I had was about 550 miles so I only had to stop once, at about 400 miles, to fill up and grab some coffee. But back then time was money, and when you are semi-retired time is just time.