One thing to take into consideration, is the stuff you buy at the grocery store ,that is not food. Soaps, deoderant, garbage bags, toilet paper, plastic wrap, etc. That kind of stuff can really add up.
If I take out the non-food items , I can reasonably budget( with out feeling I have gone without) for about $30.00 per week. That all 7 days , 3x per day... and of course the inbetweens and the occasional bone for my fuzzy one.