SP prices [stab]:
1 JOSH'S WHISKY 2.60 1.10
2 TREW FOREVER 14.80 3.30
3 ARANDT'S TEARS 9.00 2.50
4 SISCO TRAIN 21.30 4.10
5 ELIAS BALE 7.10 1.80
6 BREAKAWAY THREAT 2.80 1.40
7 CHYNNA SOLAIRE 28.40 4.70
8 ASSASSIN ADVICE 21.70

1/5/8 Tri $214
You collect on 3,1/Field/Field for $5 [8.33% of $214]


Problem is working out odds. Their SP reality is going to be way-out of wack [as above] to what you work out. As a win bet, No 1 would have been well and truely unders.

Getting decent prices might be a problem, but I like your original idea though for working out winners!