Cost of food while camping ... does it have to be high?

At the beginning of the season I stock the TT with the same things I use in the house, only smaller amounts. The freezer always has lots of various meats. The fridge with the staples always full. We add fresh veggies and fruit as needed.
When we get home I take stock and replace what we used. We eat very much the same as home. I notice no extra expense camping for food. When we head out the next time there is usually very little "shopping" to do.