you said you can't pay someone full time but can you pay contributors on a per contribution basis?

I don't think you made it clear what the bottleneck is in your compensation model. Is it the amount of funds or is it the currency? If you can pay in EUR or USD or whatever locale the contributor hails from, you should look into how magazines or online publications pay for articles. Maybe decide on a $/word amount you can afford and see the interest you get at that price point?