have a look here for real world cost of car ownership for new cars purchased on credit.
http://www.racq.com.au/motoring/cars...ing_costs_2013
Example Fietsa 1.6 47.91 cents per Km vs falcon 4.0 6 speed 88.16 cents per Km.
takes into account purchase price interest, running costs and insurances etc all explained in the document.
average 400 Km per week makes a very substantial saving per week in the smaller car!
JP