You have to get a bit thrifty and learn to be a little bit of a scavenger I think.
Farmers Markets can be cheaper than the grocery store for good organic food, but compared to conventional produce the grocery store is usually cheaper. Here's how I save money.
1) Buy in bulk- especially meat. Cowpooling, and/or investing in a chest freezer will be a huge benefit. It was one of the first things I did when going Primal. You can get tons of great cuts of meat for as little as $2.50/lb
2) Look for waste. People don't like certain cuts. I get heart, tongue, liver and other organ meats from my butcher VERY cheap.
3) Check your local Craig's List farm section. I've found local farms selling pastured eggs at $2/doz or less, chicken hearts and livers for $1.50/lb. Don't be afraid to expand into the "weird" either. I got chicken feet for $1/lb.
4) Look for a local Crop Mob organization in your area. You work at a farm for a day, and they give you a meal. Make friends with your local farmers and help out. At the end of the season they're apt to be giving away surplus produce. If you don't have a local crop mob, start one, or simply approach farmers and offer to help out in exchange for surplus during harvest, or a discount.
5) Local farm stands are awesome. Farmers markets can be pricey since vendors often have to pay to set up, but small local farms may have a roadside stand.
6) Look for "U pick" fields. You pick your own produce from the field and pay a discounted rate.
Just doing this stuff, I generally can live on less than $150 a month for food.