I think it highly depends on how well you choose the bounties you participate in. They usually pay percentage of their ICO, so the more successful project you choose, the more you earn. The rewards can thus vary widely, probably somewhere between $100 - $10k per let's say 3-months running bounty campaign.
I'm still trying to earn with bounty campaigns. It is so hard to earn with this type of work. I hope i can earn with that amount also. It is so disappoint when i compare, like why does other users earn much more than me? So i learned to just watch myself not other people