If it is really true that you need a 7000 participants for your bounty campaign then you must think of the fact that quantities will not guarantee you a success in your project it is still the quality of the participants that represent it that really matters even if you spend more to a few of them. And also keep on mind that multiple accounts are a big issue in this forum that can make abuse of that massive amount of required participant.

finding campaign manager is the first thing that you must do in able to lessen your headache with your bounty campaign and it is much better to get the well known and well experience one.