Don't expect a ton of savings, those prices are pretty rigid, so we usually just buy from Disney to ensure everything is legit.
Also, use www.touringplans.com to help plan out your itinerary at the parks, it uses historical and live data to tailor an itinerary that limits walking, waiting, or a balance of the two. You will see and do more using their system, as I have been successful with it half a dozen times.