The most expensive book illustration sold at auction is a Beatrix Potter (UK) watercolour titled The Rabbits’ Christmas Party, created in the 1890’s, it was bought on 17 July 2008 by a British collector for $513,177 (?289,250).

From BBC website: “The watercolour was one of 20 Potter illustrations, books, Christmas cards and letters offered for sale from a collection belonging to her brother, Bertram Potter.
The entire collection, the most extensive body of Beatrix Potter artwork to have appeared on the market in decades, raised a total of ?748,200.”