There is lots of Risk here both for the delivery person / company and for yourself and myself as an small investor. The bounties I have seen differ significantly in price (a new website, no idea what I want), json ticker and infographics, there is no measurement of work / plan for each actual bounty. Mainly I have lots of spare money (pts), give me something quick, I don't know how to price it but I will give you what I consider what is fair considering the risk you take.
I believe you need a clear and granular road map, and you should focus on very small bounties, each bounty should be rewarded for the completed work of week maximum, ideally a couple of days to reduce the risk for both parties.
You should borrow from agile methodologies, and match each bounty to a task in an iteration. For example building a website has many tasks and iterations, this should drive both collaboration between the people delivering the bounties plus also reduce the risk of knowledge management and key dependencies.
The owner of a particular work stream should publish the work required 2 weeks in advance to get the required people involved, ideally if you manage to get a team of 10 (ie developers) the work will be delivered by the same team with what I assume with a constant turnover of 2 people.
To cut the story short, small tasks, quick delivery, self organising teams, clear road map and most important good requirements for each iteration. Most important an iteration can be just a "mock up" of something to get good ideas of a requirement.
Hopefully it gives you some ideas or most probably I am just preaching to the choir.