It sounds like you're not afraid of cooking, so I would start collecting recipes where you can get good bulk and nutrition from relying on dried beans and grains. If I were on a budget like what you describe I would buy my favorite beans, some brown rice, some Quinoa or other high quality grain you like, some oats, eggs, and budget in some protein that you can stretch. The beans and grains will go a long way and last you a long time, then you can start budgeting more of your money for protein and fresh veggies...some good leafy greens, and maybe some root vegetables like beets and sweet potatoes. I suspect you have a reasonably stocked spice collection, and that will help a lot.
There are great online recipe sources if these are items you don't cook with regularly. Some you can just put in your ingredients and it will tell you what you can make.
I would try to buy in bulk when it comes to grains and dried beans, and if I were you I'd pick up some nutritional yeast while I was at it. I use it in a lot of recipes to get a kind of cheesy taste and it's full of good B vitamins.
Starting: 11/14/2010, 350 lbs (Yikes!)
Current : 03/31/2010, 295 lbs
Starting:1/20/2012, 335 lbs
Current: 2/10/2012 324.4 lbs
Goal 1: 302 lbs 04/01/2012 April Fools 10% Challenge
Goal 2: 271 lbs 07/04/2012 4th of July 10% Challenge
Goal 3: 247 lbs 10/01/2012
Ultimate Goal 160 lbs 05/31/2013
Lost: 10.6 lbs