Drawings & Strip Art: what are auction value?

Auction catalogs of illustrations hold real surprises. For example, 25 original watercolors by Milo Manara, dedicated to the French actress Brigitte Bardot have been sold for almost 600.000 euros (592,702 euros), by Millon Auction. Instead, copies of limited and numbered editions cost literally a thousand times less: 400-600 euros, on average.
Similarly, a small drawing by Georges Prosper Remi, better known as Hergé, is estimated at between 50 and 55,000 euros (see photo below, Christie's, 2019, Paris).
Paolo Eleuteri Serpieri (1944), the artist in the photo above has an auction valuation of 6,000-8,000 euros for drawings slightly larger than A4.
More generally, original Strip Art by more or less well-known authors has auction prices ranging from 1,000 to 15,000 euros.



Milo Manara: original 25 watercolors "Brigitte Bardot " sold for 592,702 euros (Millon, 2016)

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Milo Manara, limited and numbered edition (1/200), 400-600 euros.

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Hergé (1907-1983), original "Tintin", € 50,000-55,000, Christie's, 2019, Paris.

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