From what I have experienced in any casino including casinopunk which I played some time ago. betting at $0.2 either when getting a free spin bonus or buying it never gets a profit above $10. Either I'm unlucky or the provider I play is not that good. Usually the PragmaticPlay provider is my favorite but in the future maybe I need to move around a bit to try whether $0.2 from buy spin exceeds $ 10 or not.
Probably, you are using a slot games with less volatility and high hit ratio that’s why bonus buy doesn’t convert to anything big amount. I experienced this on game provider such as Play’n Go that gives me easy hit on bonus game but the outcome is usually same with normal spin hit rate.
You should increase the volatility of your game if you want a higher hit on bonus game. But make sure you accept the higher risk of losing since the higher the payout expectations mean the higher the risk.
It’s a high risk high reward depending on what type of game that will give you fun.