making $ 100 from working on airdrop is possible, but if you always get it every month it's impossible. because most projects have a period of more than one month.
It's possible but the chance is low on these days. I can't find someone now who does claim that he has earned $100 within airdrops at these moments but for the past it's very likely because of the emerging of projects. But now, it's difficult because people are no longer into airdrops and this is like a test but no one's willing to pay with a price if the project isn't really good. You may earn around $5-$10 and that's already a struggle.