Answer: Jefferson believed that the United States needed the Lousiana Purchase, eventhough the cost might be a little bit expensive.
In 1801, there was a threat coming from the French that if United States did not buy New Orleans from them, they might started a war.
The United States couldn't have another war, so Jefferson returned with a compromise to buy the Louisiana Territory instead of New Orelans from the French because it benefited the United States and it's people the most.
Explanation: Hope this helps!