Cost to the end consumer has nothing to do with it - it's all about how the mill did the run, and whether the supplier had anything to do with it as well.
One thing people don't realize is that an awful lot of steel comes from recycled material, so your dad's Buick is in that billet as well, and while most of the really rotten stuff burns off, I've seen streaks of copper in a bar of steel before.
If they blend all the ingredients as they're supposed to, according to the recipe, they can call it by the spec's name. I'm sure there are tolerances for chemistry - so it's not "exactly" 0.95% carbon by weight, it's more like 0.86-1.02% as an acceptable range. Chemistry notwithstanding, the cooling rates from liquid to billet, the rate at which carbon was reduced, the manner in which alloying elements were introduced, and the process by which the steel was reduced to the form you get it can all play important roles in the character of the steel you end up with. It's actually a whole lot like baking, really. 2 chefs with the exact same ingredients, following the same recipe, but sourced from different stores and using their own techniques, will make two very different muffins.