It really depends on your gaming skill, online casino you choose, and how lucky you are. All those factors affect your possible winnings. You can look at some progressive jackpot games like Mega Moolah which can give you a chance to win really big due to their nature of increasing jackpots every time the game is played and not won, don't forget to look for a better welcome bonus offer amount to get a broader chance to get your spin winnings and pick games with a higher payout rate.