That's not a good logic. There's not much relation between affording a civic and affording petrol costs. Buying a civic is not exactly an expense, it's more like an investment, something you will recover later on when u'll ultimately sell the car, albeit at a discount to the purchase price. However, spending money on petrol is a direct expense, something you can really save.
If CNG can cut my monthly fuel expense to half (as compared to petrol), then roughly I can save 10,000 Rupees per month, which is a lot of money to waste every month.