I think the term reliable doesn't really relate to cost of repairs. My car has needed some repairs lately that were a bit more costly than I would have liked them to be, but even at almost 15 years old and 180,000 miles the car has never let me down once. It has never failed to start, got me stuck, or left me high and dry anywhere. I am constantly seeing cars broken down on the side of the road (alot in the middle of the road), and all are cars newer than my own. Also, as discussed in other forums, Mercedes are not necessarily more expensive to fix. I have a friend with a Honda Accord that is less than 6 years old who replaced his distributor cap for the same cost I replaced my cap and rotor and wires (and those Mercedes Wires are bloody expensive). Just thing if you were given the job of buying all the parts necessary to build a Mercedes from scratch, compared with other cars. It would cost a heck of alot more and take much more time. But would it be worth it? You bet! I don't know of any model that is better on the maintanence budget than others. I do know that the big bodied S-Class (w140) is supposed to be the most expensive Benz to repiar and maintain since the 600 of the 60s and 70s. Your best bet in buying a Benz, if these repair costs are a concern is to buy a newer modelo with a starmark warranty. I don't know how much more it will cost you, but others on this forum say it is worth it.
1995 E420 - retired
1986 420SEL - retired