Never seen Disney discount their tickets. There are third party vendors that offer a slight discount (Undercover Tourist). There are others, but I haven't personally used them. Another way to save a little is if you purchase Disney gift cards at places like Target (with their redcard) and you can save 5%. Sam's Club offers a little discount on Disney gift cards. you could then use the cards to purchase through Disney.
You definitely want to try and purchase your tickets before your fastpass date. If staying at a Disney resort you can make fast passes 60 days out. (There are some other resorts that qualify for 60 day fast passes but their "contracts" are up December 31, 2019. Might get extended?). Othereise, it is 30 days out.
Also, it is important to know that tickets are now "date specific". If you look on the Disney site, you will select your dates and it will tell you the price of your tickets. You can do this without following through with purchase to give you an idea.