With Bitcoin Galore you can play with even just 0.00001 BTC (which is 10 uBTC) for each combo. If you are lucky you win a prize.

Each prize is divided between all the winning combos, but on average:

If you guess 3 numbers you can win an average of 0.0005 BTC (500 uBTC), which is 50 times.
If you guess 4 numbers you can win an average of 0.01 BTC (10 mBTC), about 1000 times.
If you guess 5 numbers you can win an average of 2.5 BTC or around 250000 times.
If you guess 6 numbers you can win 26 BTC and more (the game is pretty new and nobody guessed 6 numbers yet).

You can play more combos to increase the chance to win. Playing 1000 combos is just 0.01 BTC (10 mBTC).