40K Evreyday makes it stand at 6800 almost?
100K everyday makes it stand at 17000 almost?
You also need to make sure,
1- On CNG, you are not going to get everyday, your car would keep running on petrol for 1 to 2 days every week (during winter)
2- You would ruin warranty
3- You would invest 40-60 thousand extra that should also be included in CNG/km price.
4- Always in a CNG line every day (total waste of time) for 10 minutes
5- Don't know if you get engine penality and how much!
6- If you really go 100KM daily, you might save some money. 40 isn't a big deal.
If you bought a 1300CC brand new car for over a million, and you are ready to put extra 60000 for CNG, you ain't be called Poor. But its your money and you would afford, so wish you good luck if you go for CNG.