“A quarter of a million dollars is the most money ever put up for two horses to race for. This sum was wagered at Natchez, Miss., in 1836, Walker Thurston matching his horse Rodolph against Hon. J. F. Claybourne’s mare Susan Yandell for 2,500 bales of cotton aside, it being equal to $250,000. Susan Yandell had a walkover for the money, as Rodolph took sick shortly before the time set for the contest.” (The Daily American (Nashville, TN), 06/14/1890)
Accounting for inflation, $250,000 in 1836 is roughly equivalent to $5,540,000 in 2016.
Susan Yandell would go on to become the sixth dam of the Salvator colt Savable, who landed his own big cotton in winning the $58,400 Futurity Stakes in 1902.