Can I purchase the notes for only one novel such as Extremely Loud and Incredibly Close?No
Enotes' study material is available through subscription. I recommend getting the eNotes Basic pass. You get access to all thousands of study guides, critical essays, and documents; in addition, with the basic pass you can ask 3 questions a day and have access to all of the expert responses. At about four dollars a month, it's easily one of the best deals out there--some of those study guides on other sites are so expensive--and with the subscription, you have access toeverything.
I looked at the notes for the novel myself. They're excellent.