Instead of using merely power, it would be nice a list like "points in track times buck".
By points in track, I mean, you could sum the seconds of the very best positions a car has and divide this by the number of tracks it has a record on: AVERAGE SECONDS. (excluding very long or very short tracks, this number do not deviate too much... but you can use some sort of weighted mean considering the tracks' lenghts).
AVERAGE SECONDS x CAR PRICE = some number (the less the better!)