i have a civic 06 vti (manual) and it has done 775000km. it fills for about Rs 380-360(when empty).
within city(with A.C) 65-75 km
within city(without A.C) 85-95 km
long route (with A.C) 100-110 km
long route without A.C 120-135 km
and my personal advice is that u should install cng after 40,000km