Well lets go over your options (I'm assuming we are talking about similar price ranges for a civic rs and mercedes alternatives):
A W212 E class is quite a reliable machine but given its age and the nature of how the parts are connected (loads of plastic piping) you are going to run into risks of frequent visits to mechanics. Those could be super minor things like pipes being loose but also come into more expensive categories. Finding well taken care of examples may be a challenge.
A 2007-2009 S class might be in this range but you would struggle to maintain the air suspension that is bound to collapse on these pakistani roads. Much more comfort oriented than fun, although driving big cars in cities here makes me more worried than enjoy them.
A first gen BMW 6 series would be super fun, but once you have any kind of engine issues (which would be a possibility at this age) would cost a pretty penny. Electronics going haywire is always a risk with bmws but these should still be a bit on the safer side (compared to a 7 series of that time).
An BMW F30 3 Series would be cheap enough that you could keep money aside for repairs, but the kind of specs that you find here make me wonder if you would find it more fun that the Civic RS. Definitely the most fuel efficient car on the list here, but that still means around 11 km/l in the city in comparison to all the other choices that would be closer to 8-9km/l.
A Merc CLS500 could be a fun vehicle if you do not mind the age, but I would suspect you would run into similar issues like the w212 E class but with more expensive parts. There would only be a handful for sale so maybe if all options are not up to your standard this would not be an option.
Driving pleasure wise most of these cars have characteristics that are wildly different from Japanese cars. Mainly weight, as these are all rather heavy cars with rear wheel drive. Mercedes has really perfected suspensions in my opinion and just sitting in one brings a smile to my face. However, from a financial standpoint, the new Civic just makes more sense. Going into something like this is about heart, rather than trying to make a smart choice. German cars are a gamble because even the higher milage cars can be trouble free whereas low milage ones can become full of problems in no time.
