How about you have to pay more to bet for big winners, makin it less rewarding if people like doulie wins, and more rewarding for voting for underdogs
The way that its handled in real life is that the bookie will put lower odds (e.g. 3:1, 2:1, 1:1, 1:5 etc.) on a top racer, meaning that when people bet on them they win less money from it.
Something that I think would be good is if you could bet both ways (in horse racing that puts 50% of the bet on 1st place and 50% on top 3 and if they come first the top 3 bet doesn't count), but modify it so that it only counts as a win when they win or are runners up.
Whether or not we use both ways, the betting system could work so that if you win you get the winnings (e.g. double your initial investment on a bet of 2:1) plus your original bet back.
Talking of that, this has given me an idea. We could allow users to set up different bookmakers with each one watching each others odds and making modifications to their own to try and entice more bets to their bookie. That is how they work at real live events and I think that it would be like a new shop type where they are all constantly competing with one another for bets, having to pay out of their own pocket if they lose more PC than they gain. That would limit the number of bookmakers as users need to be able to afford a big loss to risk opening a bookmaker, and I think that it would be a fun little feature - moreso than a simple rock/paper/scizors (pun intended)-esque room like we have been talking about so far, and a a balance of risk vs reward.