My budget has creeped up to $140/month+$10/month for loose tea. I think this is mostly due to pasta doubling in price over the past year or so.
Anyways, the reason my costs are so low, is that food simply costs less in some areas of the country than others, I shop at Meijer. 95%+ of what I buy is on sale, and I will usually buy the healthiest version of store brand (which isn't always the cheapest). I don't buy any store brand food that doesn't taste good obviously (orange juice/waffles). I never buy red meats, but chicken and wild caught fish is usually on sale, I bulk up on it if it is a particular type I like a lot. I eat rice/pasta a lot, usually 2 or 3 times a week. I make my own sauces, a week's worth of sauces costs 25 cents, and they are very good with the pasta/rice/chicken. I buy frozen vegetables, unshredded romaine lettuce, and melon. I go through a gallon of milk every 1.5 weeks and drink tea 2-4 times a day (citron green/oolong #18/jasmine/coconut black). I buy in bulk when possible, but rarely have useful coupons.
I only buy convenience food for work, and chalk that up as a work expense. I also very rarely eat out, unless it is for purely work related reasons. I don't like drinking alcohol except socially.
Not all frozen food is bad, just watch what it says on the back. There is a type of frozen store brand french fries I get that are pretty healthy (no salt, low fat). Most frozen vegetables are just fine as well. But, probably half the other stuff is bad, especially the pizza and frozen deserts. Some of the frozen dinner's are pretty ridiculous too, like hearty man meal or whatever it is called (150% of the fat+cholesterol+salt you are supposed to have, all in one meal!)