InfoBridge published a Guide in "Fair Price Resources": 'Guide How to Calculate Fair Prices' by Ruud Bronkhorst
A practical example is given how to calculate Fair Prices for agricultural products originating from small-holders. It starts with the calculation of a Living Wage as it is known in industry (esp. textile), based on the needs of a worker to maintain his/her family. This Living Wage is the basis for the calculation of a Living Income for the farmer. The Living Income per household combined with production costs, determines the amount the farmer has to receive for his products. Based on this income needed and the actual production costs, a Fair Price can be calculated for each different crop.
An Excel-sheet is attached showing the different steps to be taken to calculate a Fair Price. The Guide can be found here