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.
Don't you think the upper limit you stated is kind of exaggerated? $10,000 USD in three months, which is around $3,350 USD per month is kinda unbelievable. This is what an average american with a good job earns per month working full time. You need to be extremely lucky to earn this much.