Bet of the week: Grand Final Quinella Collingwood vs West Coast, $12 is the best odds I found (Sportingbet).
This isn't so much a bet for what you think will happen, as what must happen first. Collingwood will play West Coast at the MCG in week one, barring calamity.
Let's take the less likely outcome first: West Coast wins, hosts a prelim, and Collingwood is huge favourite to come through the other half of the draw. Suddenly the odds are about $2.30.
Now the more likely one: Collingwood wins, West Coast starts big favourite to wipe some random team at home and makes the prelim. They might be $3.50 - $4 or so against a Hawthorn or Geelong in that prelim, but you're looking at odds of $5 - $6 overall for the quinella.
It's basically a quirk of the final 8: 1 & 4 always go to opposite sides of the draw. When you look at West Coast $5.50 to make the GF (even that is a little generous I reckon), and you know Collingwood is always on the other side of the draw, how does Collingwood vs West Coast blow out to $12?
How do they blow out? Because they have no chance of beating Geelong or Hawthorn in Melbourne.