Costs are down at my house, especially if you count the reduction in eating out.
I used to spend $15/week for lean cuisine for lunch, and we would eat out 1-2 nights/week. Weekends were crazy with fast food for lunch etc. Now I cook meat and veggies, or salad at dinner, and bring leftovers for lunch.

My cart is filled with meat and veggies, but it helps that my husband is a hunter and a fisherman so my main costs are salad, chicken, and pork. Eggs are cheap, and we go through a lot every week. I even splurge and buy brown eggs, and it comes out cheaper than a cart filled with chips, crackers, cookies, low cal breakfast bars, and other prepared foods.

I usually just by the meat or veggies that are on sale, we eat both fresh and frozen veggies.

I don't buy any specialty low carb products. This is a place where LCing can get expensive.