There is no fixed price on how much you can earn on signiture campaign
Why? It is because the earning depends on how you do your job accordingly to the rules of such campaigns and by these you will get some stakes and at the end of the campaign these stakes will be sum up and divide to the token allocated for the bounty program.
But on some campaign they tell how much a participant can earn
As i can recall Jr. Member will recieve approximately 110-210$
And for memeber is 210-310$ thats what I remember if im not mistaken
Good posts, pay attention to them

Also, take a look at this link that summarizes all the campaigns that are happening:
https://bitcointalk.org/index.php?topic=615953.0?Another tip worth repeating
is always following the campaign rules.