I'll bet you are actually spending less shopping once a week, v. running to the store all the time--I know I do. I spend around that much, maybe a little less, for the four of us (dds are 2 and 5, but I think the kids really don't add much to the bill).
Is this just for food, or does it include other things like toiletries, pet food, cleaning products, etc? Those things are generally cheaper elsewhere than the grocery store where I live, but I often don't have the time to run to other stores. They can add a lot to the bill.
If I can run around to different places to shop, I can save a significant amount of money. I work out of the home though, and my shopping time is pretty limited. So when I do get to stop someplace that has a good price on certain items, I tend to buy in bulk. I have a freezer which helps.
If you really want to trim your bills, check out the copies of the Tightwad Gazette (3 vols) from your library. The author makes the case for really keeping track of prices of things that you use all the time and finding good places to shop. There generally is no one cheapest grocery store. You save the most by shopping different places, but it does take some time and some planning so you aren't running all over the place, but make stops to pick things up as part of your normal errands.