It wasn't that long ago that I read an article on a couple who went to the limits stretching the food budget.  I wish I could remember the name of the article, because it was interesting to see how they did it.  One strategy was finding stores that would let them buy food that was about to go into the trash because it was at or just past expiry date.

Anyway, do a Google search on  "couple eating for 100 per month".  You'll get a lot of hits about how to do this.