I have had my SL500 for 3 years shortly,,but very hard to give the running cost. I have spent £3k in that time on things that have broken,,2 x struts and 2 x SAM's. Other cars can fail on other things, some do not fail at all.
I bought mine at 14k miles, so a low mileage may not help, others have had water leaks, etc in the boot,,but all of these things can be done your self.
I think that you could allow something,just in case.
They are wonderful cars and I love mine,,its fully loaded
On the service side, I have had one A service at £300 with MB at 23k miles, and the B service with and indie at £200 at 35k miles.
Tyres on the 500.. the fronts will go up to 20k miles but the rears on wide tyres go about 14k miles.
The rear disc are the original at 40k and still good. the front went odd in the way that drilled disc can, so I replaced them at £100 for the pair. I cant comment on the Pads as I use EBC to keep the wheels clean, and they have been in for 20k miles and still good.
With luck and you get no strut problems then not too expensive to drive ,,fuel can be as low as 17 on the 500 to 29.9 on a run
Yes should be fine. I got my insurance with Mercedes insurance as they were ½ all of other quotes.
Using the forum we can direct you to the lowest possible running cost.
The 350 is much cheaper to run, as it does not have the same suspension, and cheaper on fuel too and service, and 1 or ½ a sec slower up to 60mph, the 06 car is the 350 to get.
They are wonderful cars,,most of them do not go wrong, get one with a warranty and you will be fine