Single or multi-day? And what are your trip dates?
For single day tickets, there are rarely discounts. Right now, if you know an annual passholder, s/he can buy you a discounted, single day parkhopper ticket on a day that her/his pass isn't blocked out. And the passholder must accompany you the first time you go through the turnstiles. Otherwise, the best place to purchase single day tickets is through Disney, either through their website or their app. Then you'll be able to skip the ticket booths and go directly to the gates.
For multi-day tickets, LMT Club (do an internet search for a free membership code) usually has the lowest prices. Also check Mousesavers.com to see if there are any other deals that might work better for you. All of the ticket vendors they recommend are legit.
The worst place to buy DLR tickets is from an unauthorized vendor -- beware of getting scammed!