I been playing around with what The Elk posted and I came up with this.

(Available Odds/Rated Odds)-1
Multiply that by 100 * Rated Odds

The 100 figure can be replaced with any suitable number that allows the Bank to withstand a losing run , and to keep the Punter within his comfort zone.

In the example the wagers would have been like this.

2 ROCKADORE 80 cents
3 SISCO SPICE $13
8 MAGIC PENSKI $1

All Other runners have negative results in the Formula so don't qualify.
It would have been a loss of $15

But the available Odds posted were from the Form Guide , and the actual Market Odds available were such that the actual wagers would have been $6.50 on the Winner #4 @ $2.90 and a couple of 50 cent wager losses.