You can easily calculate price. Or, well, you can just go see what people are asking for and/or charging.

You can't easily calculate labor. People try this kind of thing all the time (e.g. with carbon footprint) and you very quickly get lost in a web of interdependencies. Thus also with pure labor let alone socially necessary labor.

If there is a distinction between price and "true" exchange value (determined by socially necessary labor), then the latter is really hard to calculate accurately.