I don't recommend this especially if the airdrop has a continous task involved, if you're going to refer it should be people who have similar interest on airdrops, these paid referrals will just become dead referrals because they joined because they are paid to do things for a few cents and do now want to be actively involve in a project where they are not familiar with.
If you want referrals there are a lot of groups who are into airdrops on social media if you can explain its potential they will trust you and agreed to be your referrals and even thank you.