Short answers, pulled from the story.
The final handover to American officials took place on the 20th of December 1803. A transfer ceremony occurred on the 30th of November 1803, just three weeks before the formal sale to the United States.
Napoleon abandoned plans to rebuild France's New World empire after more than two-thirds of his 7,000 troops died from disease and fierce resistance during the expedition to Saint-Domingue. War between France and Britain seemed unavoidable by March 1803 when he began planning an invasion of Great Britain, making peace necessary to take possession of Louisiana effectively.
The total cost reached twenty-three million three hundred thirteen thousand five hundred sixty-seven dollars with interest. The original price was fifteen million dollars paid through bonds carrying six percent interest redeemable between 1819 and 1822.
Napoleon told Treasury Minister François Barbé-Marbois about considering the sale on the 10th of April 1803. Four days later, Barbé-Marbois offered Livingston all of Louisiana for fifteen million dollars while American representatives had been prepared to pay up to ten million dollars only for New Orleans and its environs.
Louisiana Purchase negotiated between France and United States without consulting various Indian tribes living on land. Four decades following purchase era involved court decisions removing many tribes from lands east of Mississippi River, culminating in Trail of Tears movement during mid-nineteenth century.