$1 bonus buy would be the cheapest buy bonus ever in the industry unless I miss there is any other slot games with that low buy bonus.
For a game like Sweet Bonanza, $1 is too low if you ask me.
Perhaps $5 would be an ideal price for average gambler, at least it gives an alternative for those who want to play Sweet Bonanza but they cant afford to pay $20 for the buy bonus.
The bonus buy is based on the base bet, so if the game can have 1 sat minimum bet, they can set the bonus buy with 200x minimum bet (hence 200 sats) or whatever. Yeah it's too low, but that's the nature of hash games.
Another advantage is you can vary your base bet to get the dollar amount that suitable for your taste.