Honestly, $200/month for 1 person is very doable!
I'd recommend looking in our shoestring meals area:
http://www.3fatchicks.com/forum/shoestring-meals-235/
My budget for myself and my husband is between $250-$350/month and that includes a lot of organics. I cook almost all our meals though and I rely heavily on beans and whole grains as we don't eat meat. Hopefully the nutritionist can help you. I have a friend who is a dietician and part of their program required them to work out low budget meals. She said she was given $30/week to create a nutritionally sound diet and she found out that she actually only used $15/week. Beans were a staple of her weekly diet plans but there are so many ways to use them.
Also, don't beat yourself up for where you are but trust me, as you start walking, getting more exercise in, you will be surprised at your progress.