Please mention the city where you want to buy this car as prices varies across cities. However I am providing you the details as per the ex-showroom New Delhi.
Currently Nissan Micra is available with four variants - XE (the base variant), XE Plus (Base variant with some optional features) XL (mid) and XV (the top end) which are priced as below given price list.
Nissan Micra XE - Rs 3.98 lacs (ex showroom Delhi) - Rs 4.28 lacs (on road Price in Delhi)
Nissan Micra XE Plus - Rs 4.25 lacs (ex showroom Delhi) - Rs 4.69 lacs (on road Price in Delhi)
Nissan Micra Xl - Rs 4.69 lacs (ex showroom Delhi) - Rs 5.19 lacs (on road Price in Delhi)
Nissan Micra XV - Rs 5.28 lacs (ex showroom Delhi) - Rs 5.84 lacs (on road Price in Delhi)
For more details of the car along with its ex showroom and on road prices in your city you may visit the given link of Micra.
We encounter similar question many times, the easiest way to increase the mileage is to keep your car healthy. Keep the tyre pressure proper, air filter clean, always follow speed limits and turn off your engine on traffic lights. Find more tricks here- Please find the details Chevrolet service centers here- http://forum.cardekho.com/topic/356-how-to-increase-mileage-of-your-car-tips/
There is not any special petrol recommended for NIssan Micra. You can use simple unleaded petrol in it. However, you can use Speed, Power or Extra premium petrol for better performance of the vehicle.