The Mona Lisa is priceless. Any speculative price (some say over a billion dollars!) would probably be so high that not one person would be able or willing to purchase and maintain the painting. Moreover, the Louvre Museum would probably never sell it. The museum attracts millions of visitors each year, most of whom come for the Mona Lisa, so a steady stream of revenue may be more lucrative in the long run than a single payment. Indeed, the museum considers the Mona Lisa irreplaceable and thus spends its resources on preventive measures to maintain the portrait rather than on expensive insurance that can only offer mere money as a replacement.