It used to have very good sale, not anymore. I sold my 12k Euro II 2012 Nov registered Mehran at 570k, bought @ 593k, A/C & DVD player was added which didn't paid off.
Buying new Mehran will eat up a lot of fuel as the engine is new. Even 3500 Mehran is still considered new engine. 12 km/l is good with in city, in the later days, I used to have maximum 10 km/l which my vitz is giving me now. On highways, I got from 11km/l (motorway as I drove it around 130 ~ 140) to 18km/l on Multan ~ Lahore highway (avg speed 90 ~ 100).
If you want economy and want to drive within city, get JDM 660cc, will save you a lot of fuel, else get vitz 2005, its good with fuel too, better than Mehran.