I have only ever played with this idea and never realy tested it to any degree but you could try this...take the top 6 prices about 5 minutes to jump and and put your bets on line this.
1st/2nd
1st/2nd/3rd
1st/2nd/3rd/4th
1st/2nd/3rd/4th/5th
1st/2nd/3rd/4th/5th/6th
cost $35...i tried this on the dogs at one point with some success