Even that fluctuates frequently. When I worked at a grocery store, when you ordered something it would show you what the item would "cost" the store.

This could change from day to day (e.g. fruits, veggies), vary based on quantity ordered, etc.

Then you get into private label (store brand) products, where the "cost" was usually either $0 or some ridiculously low number.

This was a national chain. At the store level at least, we wouldn't have been able to find the value of an item "at cost" with any confidence.