How much is a painting of Dedham Mill by John Constable worth?

Salisbury Cathedral from the Meadowswas painted by Constable in 1829, one year after his wife's death. He later added nine lines from "The Seasons" by 18th Century poet James Thomson that reveal the painting's meaning: That the rainbow is a symbol of hope after a storm that follows on the death of the young Amelia in the arms of her lover Celadon. To paint this picture that was commissioned by the Bishop of the cathedral, Constable made four oil sketches as preparatory studies for the real painting which was planned to be big (151x180 cm). Those four sketches were offered on auction in 1981 in London : one of them went for £ 324,000 ($518,400).