The Follower Factory
Devumi is a reseller. Services they use are near 0.1/1000 follower, even less, with pool of 200k+ users per Services, 3/4 pools (just use Google, for Facebook many are even real, collect tokens is fairly easy). And people that sell these services at those prices, are reseller themselves using API to control those bots, in really EVERY services you think about (even telegram); revenue made by likes/etc may be really a small part, just think about the power in elections + the the really small price