Collecting People to Join a Game Contest

I need to collect 50,000 (fifty thousand people ) to join a game contest. The game is online and provided at google playstore. Free to download but every person need to pay for about $2.7 to join the contest. the prize for winner is cash. Could you help me to collect 50,000 game contestants before the contest starts? The remaining time is about 2 - 3 months.