Is there a prize for all participants?
There is a 30mBTC freebet or 90 mBTC (for 1 BTC + bankroll), as long as players have made the minimum amount of bet slips during the competition.
As for the minimum ammount of bets, here are the rules that explain how you could qualify:
5. A minimum of 70 bet slips must be made during the competition to qualify for prizes.
5.1 The minimum number of bet slips required to qualify can increase if your largest winning bet is won at odds above 35.
In this case that minimum will be two times that odd.