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?

A few hundred dollars is not a big deal for bounty hunters. Many people earn wages of $ 1-2k per month for their work. I recommend moving on to bounty campaigns and making money from it. ICO projects are very much and the bonuses are a lot.