Like you said there are many people do it for free for open source projects. Why not try to figure out the reason for them to do so and do so for free? With tha

Like you said there are many people do it for free for open source projects. Why not try to figure out the reason for them to do so and do so for free? With that reasoning, I believe you maybe can find out some changes to the "job" or the "company culture", or the "expectation from the management", or something else that could help you attract more candidates.