I had 2012/15 Mira e:S and it used to give me around 18-20 kmpl mileage in the city with AC, although, being the 660cc, you can't compare its AC performance with bigger cars, the performance was optimal for the city in hot weather.
By the way, in your budget, you can easily get the newer model Mira e:S and I have heard that it's even better in terms of fuel average.
The rest is your choice.
I hope it helps.