$100 isn't really costly for the devs if they actually gathered hundreds of thousands to millions of dollar during their sale. The portion of bounty budget allocation is just a small amount to the whole that they've collected.
Maybe someone with some experience in send to multiple eth addresses knows. You also need to use a special service or have the know-how to send to multi addresses as well.
AFAIK you need to create contract like this website:
https://multisend.co/