How much is a painting worth?

Having recently read that an abstract oil painting by Chinese-French master Zao Wou-Ki sold at Sotheby’s for $65 million and a work by David Hockney, Portrait of an artist (pool with two figures) was given a sale estimate by Christie’s of $80 million then actually sold in November for $90 million I am beginning to wonder just how much is a painting worth?

David Hockney isn’t even dead so for a living artist, it is a ridiculous amount of money. Ok, he is 81 so there is a reasonable probability that his works are going to become more scarce. As to be fair, he isn’t getting any younger.

We are talking ridiculous amounts of money here. More than any average family could earn between them in a lifetime.

How could such a price be justified? How can anyone be allowed to spend such ridiculous amounts of money in the first place on what to some is just another possession or expression of their wealth?