There is a lot of misinformation and assumptions in this thread! In addition to the very helpful post a few above here:
• Disney is not charging $3500 for a melted Vader helmet; Propshop is.
• Disney would not have compelled Propshop to do these props.
• Disney has already made their money, in a one-time deal selling Propshop a license to produce and sell these items.
• The cost of these items is not due to the production process - it's that aforementioned license and a short run. The license would be very expensive, and if you're only going to make 500 Vader helmets, the cost of that license is not spread out very far. Compare that to Anovos, doing a wider high-quality run of props or Hasbro, producing tens of thousands of retail items, and you'll see a correlation in the scale. The license is the most significant cost going into these Propshop items, I'm sure.
• Just because they 3D print the masters for these replica helmets doesn't mean the end product is 3D printed. It would be a crazy amount of work to finish each one and impossible to do make the run appear perfectly consistent. That work could be done just once and then replicated through molding and casting, and I have to believe they're producing them this way.
• We know that the film's production did buy several original Graflex 3-cells (from an RPF member, no less!) for the hero sabers, but Propshop created many stunts. I wonder how similar this is to what they produced, or if they tried to make something closer to the hero prop.