And when the lower priced selection wins ?

Dutching in your head is easy : Work it out on a sought $100 win return [if you want to win $50 halve your bet amount etc.]. How much do you need to put on to win $100 when a horse is paying $10? How much for $5, $2.50? If you can work that out, you can work out [close enough] any figure. If you can't, go back to my point about the importance of understanding staking. Do that on all your horses and add your total bets. Thats what it costs to win $100 regardless which horse wins.