It was a Leonard Da Vinci. It doesn't get much more valuable than that. I can understand it being $40M. You're talking about one-of-a-kind, never to be recreated, touched-by-the-master-himself. Yeah. That I can understand.
There's a lot of other stuff in the world that's overpriced for what you actually get. There hasn't been a car made in the last fifty years that was worth more than $5000. Neither Intel nor AMD have made a chip that was worth more than about $20/ea. There hasn't been a console/handheld that was worth more than $75 in the history of the industry. Most of us, however, have paid much more for any number of these things.