The whole organic food debate is a pretty serious economic issue right now, especially since California is now considering passing a law requiring all genetically enhanced/engineered products to carry a 'modified foods' label. Organic foods represent millions and millions of dollars worth of industry.
For your comparative essay, you should start with some basic research on price points between basic items, so you can compare overall cost. I recommend that you take a trip to your local grocery store with a calculator and choose between five and ten items to compare such as: tomatos, yoghurt, milk, eggs, other types of produce. Analyze the cost differences, and then you can add your own 'hands-on' research into your paper. Additionally, you could then visit the website for the producers of the organic products to read up on their organic methods and process to see how it compares to the other farmers.