Franck you should assign people that are playing a number and then base the winnings on something no one has control over like the stock market.
Say you have 40 people. Everyone gets a number from 0-39. Then take the whole number for the Dow's close every Friday and divide it by 40. The winner is the person who's number is equal to the remainder (0-39). If it divides evenly then the winner is the person who's number was zero. If you do this no one can accuse you of cheating since we all can look up the Dow's close. All you would need to do is post the numbers assigned to everyone who's in your game beforehand.
