Building instructions - Note that the hoppers feed into droppers, and each dropper should contain 1 stackable item (e.g., 1 piece of dirt) and 1 non-stackable item (e.g., 1 wooden shovel).

This is a pretty simple (and lucrative) design I came up with a few years back, just 5 hopper-dropper randomizers connected up to pistons.

As with all gambling games, the payout structure is the real key here. "Output" is the number of sand that pop up, and Payout includes the original bet (so for 3 sand, the player would profit 0.5x their original bet):

Payout Scheme

Because the player re-rolls on 0, there's a 16/31, or 51.2%, chance of winning any given press, meaning the player is more likely to win than lose on any given press. Accounting for the 1/32 chance of a re-roll, the house has about a 10% edge:

House Edge