ok ...
CDG definately did their sums ...
If you OMO, clocking 350km on a sonata, your daily cost is
rental $101 , fuel cost abt $36 (350 / 11 x S1.14) assumming FC
for sonata is 11km / ltr
so total cost for running a sonata daily is abt $137
If you take i40,
rental $120, fuel cost abt $26 (350 / 15 x $1.14) assumming FC
for i40 is avg 15km / ltr
so total cost for running a i40 daily is abt $146
But flag down for i40 is $3.50 , assuming you did abt 30
trips ,some peak, some normal , you would have got abt $10 extra
just taking advantage of the increased flag down ...