It's a clever wheeze of an exhibition: you stand there faced with two related art objects, such as a Degas oil and a Degas pastel, or a modern forgery of a quattrocentro Madonna and a real one, or a Toulouse-Lautrec lithograph produced by the artist and a commercial mass-produced print, and then you can pull up a little sliding panel underneath to see which has an auction estimate of pounds 20m, and which has no auction value at all.
Apparently the curator has been receiving hate mail from people who believe that art shouldn't sully itself with such base considerations as prices. When I heard that I was amazed and delighted.
Who are these people who believe that art is above and beyond money? How have they managed to preserve their glorious idealism? How have they lived through the late 20th century and remained unaware that there is nothing about visual art, not a single successful artist or artwork or movement, that hasn't been turned into a commodity on roughly the same level as a limited edition Prada bag?
Money shapes people's attitudes to art, reminds us what to look at and what not to look at, whom to respect and whom not to respect. Indeed, by making that value system explicit, the Courtauld exhibition lets its visitors off the usual difficulties of people visiting a collection of disparate works, some valuable and some less so.
You can see those people in, say, Kenwood House on a rainy Saturday afternoon. They walk around the rooms anxiously, worried that they might mistake the Rembrandt for any other dullish portrait of an old man, or waste their time gazing at some anonymous 17th century interior when they have heard there is a real Vermeer in the house. Even before they look at the paintings, they look at their labels, and when they see the names they know they heave a sigh of relief, and stand there, their eyes resting for the requisite half a minute on the recognised old master.
Many of us have so lost touch with our ability to enjoy art that we must be reassured that what we are about to look at has a vast monetary value, the ability to command millions at auction, before we can spend time admiring it. And that is why gallery visitors, rather than tramping around mixed exhibitions where they have to make decisions about what to look at, much prefer the huge blockbusters concentrating on a single artist, the Monet or Cezanne or Vermeer retrospectives, where they know that everything has already been vetted - everything is very, very expensive indeed.
In the Courtauld exhibition that anxiety is made open, so that people can immediately be comforted. Confronted by a "real" Toulouse-Lautrec next to a "fake" one, or a cheap Renaissance goddess next to a valuable one, visitors can quickly shunt the little panels underneath to see what, if anything, they should be admiring.
Some might think that the Courtauld exhibition misses a trick by confining its scope to art produced only until the end of the nineteenth century. The much-hyped financial clout of art may warp our attitudes to art of the past, but that is nothing to what it does to our perception of the art that is produced today.
Although actual figures rarely intrude into the moment of viewing, as they do at the Courtauld, art's financial value is the one thing that seems to command undiluted respect from audiences now. Most people may not think that arranging two fried eggs with a kebab or painting a series of coloured spots is particularly impressive or exciting any more, but what does look impressive and exciting is the amount of money some people can still extract from governments and galleries and individuals for playing those well-known games.
Do you remember that old question: "What is art?" The answer to that changed long ago from being anything that artists think is art, to being anything from which artists can make money.
It's extraordinary to think that this century began with artists in rebellion against bourgeois values. For a long time artists wanted to carve out a space which presented an alternative to the commercialisation of the rest of society. They wanted to dissent.
Some chose to do that simply by living in a world in which the relationship of the artist to the work seemed more important than the relationship of the artwork to the buyer, turning away from the loop of careers and security and success. So Cezanne wondered: "Is art, then, a priesthood, demanding pure beings who belong to it completely?"
Others chose to make more directly rebellious gestures, aimed at questioning the idea that an artwork could have commercial value. So there was a time when to place your signature on a ready-made object - as Duchamp did - was to do it in the hope that the whole system by which art was turned into commodities would come crashing down. But as the clamour of commercial demands has got louder, what artist doesn't place him or herself firmly in the marketplace?
The attitudes of Cezanne or Duchamp, once the quintessence of modernity, now look charmingly old-fashioned. Artists today see that, in the words of critic Peter Schjeldahl, their predecessors' anti-commercialism had "roughly the impact on capitalism as a beanbag hurled against cement".
They may repeat the rebellions of the past, but in the sure and certain knowledge that the impact of the gesture will be nil. After all, it's only the first time that a ready-made is put in a gallery that it has any revolutionary value. Once the next pile of bricks is sold, and the next toilet put in a gallery, and the next tin bucket is given a grandiose title and sent to the Tate, then the revolution has turned into a money- making game.
And what artist wants to stop the game now? If the marketplace they affect to despise will pay them good money for affecting to despise it, they can have their lemon polenta cake and eat it too.
Artists today - who are, no doubt, only the artists we deserve - preserve the gestures of the old avant-garde rebellion. They have seen how it helps their marketing strategies if they act rather like the bad boys and girls of art in the past, because that is how people have come to understand art, as a series of mini rebellions that can be quickly co-opted into publicity and promotion.
So they do their little imitations of the Dadaists. They might, as Sarah Lucas did recently, put a toilet in an exhibition - oh, my dear, how too too shocking! They might, as Tracey Emin did, get drunk in public and swear on television - oh do look, how daring, it must be a real artist! They can, as Damien Hirst does, say nasty things about the media, to suggest that he is on a rather different plane.
And having made those gestures of fake rebellion, they are free to spend the rest of their time advancing their careers, having dinner with PR executives, designing restaurants where television presenters can drop pounds 100 on a meal, or giving interviews to Vogue about shopping for a silver lambskin coat.
The Courtauld is right to call its exhibition of pricing strategies "The Value of Art". The great inspiration for artists now is not lonely Cezanne or rebellious Duchamp, but Andy Warhol, who said: "Being good in business is the most fascinating kind of art. Making money is art and working is art and good business is the best art."