hello, I want to know from people who have been working in bounty projects for a long time. how quickly and effectively to gain a lot of subscribers in social networks.
If it is on twitter some people tends to follow back when you follow them, but I don't know any other ways to gain subscribers and followers since I am not that fond of social media campaigns.And with how many subscribers does it cost to work in the bounty? 
It depends on the campaign you want to join, it should be stated on their bounty thread. You can earn some altcoins via social media campaigns with as little as 100-200 followers and above sometimes.