eBay perhaps?

You might want to try your local and not so local Blockbuster and/or Hollywood Video stores. Since these stores usually carry an inflated price on their stock, they don't sell copies as quickly and may have some still available. You might also want to try some other out of the way shops and hit the used places every once in a while. Most reputable used CD/DVD stores won't inflate the price of a used disc even if a title is out-of-print.

Help Me. I'm trying to get all of Disney's platinum editions.  Can anyone tell me where i can get Snow White and/or Beauty and the Beast for a reasonable price.  (I'm OCD and I need the whole collection!)