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?

Neither the bounty nor the airdrops are designed to make a big profit, it's like your startup in the world of crypto currency. On this you need to accept that you have at least such a profit and you can exchange it for other coins.