There will be no problem with this airdrop if you ask us to pay a fee for the transfer of airdropped coins and if each user will get equal amount or amount depends on bitcointalk forum rank. But this is more like ICO because you will airdrop coins only to donators and equal to donated amount.

So this is DONATION or ICO but for sure not AIRDROP.

Common guys, I understand that sending airdrop cost some money but you have earned enough to cover this.