How much you can earn for your generosity is up to you. Here it is important to choose the right campaigns, promising, depends on how much time you spend on this work and on the number of bounty campaigns. Income may be different. I have been doing this for the 2nd year and can be said with the result. The only thing that last year was more successful in this activity.
I fully agree with your opinion, the choice of a bounty company is very important, you need to do an analysis before starting work, but now it depends a lot on luck because many projects pay a penny.