Fuel consumption and cost

I have been looking into changing a bigger car due to a growing family and hence was looking at all the cost.  The bit that intrigues is the cost with respect to the fuel consumption.  The calculation is based on a monthly 2100km and fuel cost $1.86 per litre. 

My current car consumes 15 km/l and if the next car's fuel consumption is 9km/l,  there is an additional cost of $173.60 or a 66% increase in the monthly fuel cost.  Food for thought.