Coming up with the odds are difficult.
How about a competition $25k entrance fee, predict the top 10, get 3 points for correct team, position and player 2 points for correct team and position and 1 point for correct team, so you also have to try and predict any trades you believe may happen. Winnings would be equal to entrants x 25k.
Also another competition with the top 32 predicted, but confidence style, so you're 100% certain Clowney is a 1st round talent you attach 32 points, you think there's a chance Kelvin Benjamin may be drafted in the first you put 1 point to it.
Just some ideas rather than plucking numbers out of my ass.