I've joined the airdrop over the past 3 months and I only get very little value from the airdrop, the majority of which I have to keep it to add value.
So how can I earn a few hundred dollars a month if the bounty is a good plan?

Well it depends on the project, sometimes a project become successful and listed in exchange and you can dump your coins. I advise you to choose wisely who'se project are you in, as a bounty hunter we are also need research about the project that we goin into.