Wait for a few days. Follow this thread for confirmed prices and launch dates of new corolla
Maybe you will get a basic corolla at a reasonable price ,you can easily install cng and as it has a good resale, sell it next year if you like the new upcoming 2015 honda city and buy that.
If you buy a city now, it will be replaced with a better and more well equipped car in a year
Swift is too heavy on fuel if fuel economy is your concern .and CNG will have its own issues.