my trip from isb to mirpur is 140 km
on idsi cost is
350 rps on cng
900 on petrol
1000 on petrol
so there you can compare the difference
not every one gets 18km/l on idsi... i have witnessed only a few claimers.. that too just on pakwheels not in real life.. so dont expect a miracle if you buy idsi..
and 9th gen civic claims to do 15-16 on econo mode.. which is pretty good if it really does