I'm not sure about the fuel average but based on the fact that it has a 796cc engine, I'm sure that it will be as good as Mehran, and the maintenance cost is also very cheap just as Mehran.
Still, the overall ride quality and comfort level in Suzuki FX is not as good as Mehran and as you have to travel 70-80 km per day, I would suggest you save some more money and buy Mehran.
The rest is your choice.
I hope it helps.