Clearance sections are your friend. Especially if you don't want to buy secondhand. Everything goes on clearance eventually. There are also places like the Mattel toy store in Middleton, WI that sell "damaged" goods. I put "damaged" in quotes because most of them just have beat-up packaging and the product itself is perfectly fine.
In all honesty, I'd struggle to class someone who has a massive collection of mostly secondhand Disney merch as a Disney Adult. Part of being a Disney Adult is urgency. They need everything new the instant it comes out. By the time something goes on clearance, there's something new that they need to have.