Organic food is difficult. You can't really consume less food but you can simplify your diet. Instead of thinking you can't afford organic food because you can't buy the meat or milk, change your diet to include more of the organic food you can afford, like lentils and rice. We have tried to buy produce in season and through Farmer's Markets whenever possible. Another option is Community Supported Agriculture.
People buy shares in a farm and then get whatever is ripe on a weekly basis.
And of course gardening. Even a small apartment can support some herb plants, sprouting or a tomato plant in a pot. These may not be as cheap as frozen vegies, but they are more affordable than you may think to get some fresh, pesticide free food in your diet. Even though many frugal choices are also ethical choices, there are times when you simply have to pick one over the other. The circumstances of those decisions are so varied it is hard for anyone else to say what you should do.