The total budget of a bounty campaign is divided by the number of participants. The income in various signature bounties is entirely different, but on the average, a participant with the "Member" rank can get about $400-$500 per month. Participant in social bounties, like Twitter and Facebook, can count on an income of about $20-$50 per month since participation in such campaigns is much simpler. But you may participate in many of these campaigns simultaneously, in which case your income will multiply many times.
But there are some risks, though. As not every ICO collects even the minimum amount needed for a successful completion of the project (soft cap) and in this case you don’t get anything. You should approach the project from the investor’s point of view, since even if you don’t invest your money, you still invest your free time and your effort.