When I was in college I lived on no more than $20/week in groceries. I'd look for old Sunday papers in my building's recycling bin and steal the coupon inserts. My big trick was getting food practically free by finding it on sale AND using a double coupon. Take that!
If you're a cheapskate like me, you'll look at organic produce or grass-fed beef and choke on the pricetag. But here's a different way of thinking about the cost of sustainably grown, organic food:
"The ninety-nine cent price of a fast-food hamburger simply doesn't take account of that meal's true cost--to soil, oil, public health, the public purse, etc., costs which are never charged directly to the consumer but, indirectly and invisibly, to the taxpayer (in the form of subsidies), the health care system (in the form of food-borne illness and obesity), and the environment (in the form of pollution), not to mention the welfare of the animals themselves."
From The Omnivore's Dilemma