The amount that people are willing to pay to prevent the Mona Lisa burning is proportional to the amount that the Louvre spends on fire prevention, etc. You can

The amount that people are willing to pay to prevent the Mona Lisa burning is proportional to the amount that the Louvre spends on fire prevention, etc. You can put a value on anything, even if only implicitly. It's silly to call something "priceless" (except rhetorically.)