$300 just buys you a half day of developer time, I suspect the sponsor wants a proper professional job done that works with and is tested with a range of hardware.
In most parts of the world, that's an extremely high level salary and could easily fund most peoples month, granted they live outside of Silicon Valley.
I'm sure many people would be more than happy to receive 300 or much less for half a day of work.
The $10,000 bounty is about right for this sort of work. In fact it might be a little low, but I have no idea how OBS works internally so I could be completely wrong.
Your talking windows audio /video internals which is not a common skill