That's a tough one. It get's harder to answer if there isn't enough cash to pay yourselves what you think you're worth. It depends on your lifestyle and so forth. How much do you want to leave in the business for expansion and replacement of equipment?

http://www.farmdoc.illinois.edu/

Here is a link to U of IL site that may be helpful. You could also talk to local extension personnel for ideas. If you are thinking along the lines of differentiating pay among yourselves then you need to describe jobs and arrive at a pay amount for each-what would you have to pay an outsider to do a particular job such as feeding livestock or driving a truck or working on equipment or keeping the books or marketing or....

If differentiating pay is what you're after good luck-but it is the correct way to do it IMHO. If you're all still young it will be easier to do than if you're already set in your ways.