The only difference between both CNG variants is that LXi CNG Optional comes with an additional passenger airbag. So, for safety point of view Alto 800 LXi CNG Optional will be a good option.
The exact information regarding the CSD prices of the car can be only available at the authorized dealerships. We would suggest you to visit the nearest authorized dealership for further information. Click on the given link and select your city accordingly for dealership details.
