I am mainly playing a little bit with one account, and delegating another account to a player where we split the DEC earnings. I occasionally sell some cards too.
A lot of the ROI is in the appreciation of card prices, but that is primarily unrealised gains.
The earnings that I cash out are mostly in the form of DEC which comes through daily quest rewards. It’s hard to estimate how much DEC I earn as it varies a lot, but maybe something like 20k-50k each month, around $10-$20, plus occasionally I would receive a card in the daily rewards that’s worth a bit more, like $20-$50.