How about if we were selective and only picked races where the fav was expected to be more than (say ) $3.00 and at least eliminate the killer short priced faves.
So work on only 2 rules
Races where there are x amount of runners, and
Fav price =>$3.
Possible 3rd rule back top half of the field (pricewise) (one of your old ones I think Michael?)
Cheers.........Manc.