The agreement signed by Bonaparte himself (the links take you to the original documents) cost the United States $15 million to nearly double in size. It was one of the best deals an American president ever made.
Not everyone agreed with Jefferson’s desire to expand (including his 1805 plan to buy West Florida from Spain). Why did America need more land? And not everyone agreed with the purchase price. Why spend so much?
Others supported the President’s plan of expansion. Gen. Horatio Gates told the President:
Let the Land rejoice, for you have bought Louisiana for a Song.
Soon Napoleon had more money to fund his quest for territory - nearer his own country of France - and the United States was free to explore its new, mostly unmapped and unknown land. (The link takes you to the actual map the expedition used. Lewis, it is believed, made notes to the map later, as he received information from trappers and Native Americans.)
St. Louis was the scene as France transferred ownership of the "Upper Louisiana" territory to the United States on March 9, 1804.