Why do you want to keep the pay rate private? Are you planning to pay different rates, based on the contributions of people from different countries or would you have a standard rate for all contributors. It would just be fair not to exploit people from say 3rd world countries by paying them less than people from first world countries. I had a look at your site and it looks very professional and the choice for your domain name is 100% geared for broader discussion. which is clever. 

Good luck with the site.