My dad is and has been a precision plastics mold maker for his entire career, and has been called out as one of the best in the nation many times. He’s worked on things ranging from Bic pens, to private and military aerospace components, medical equipment, and so on. I asked him about costs for making a phone case, and he told me a proper Made in America two-step process mold would cost ~60k to make. From there, costs to run it depend on where you run it and where the materials are purchased from. A two-step process is the type with a firm/ridged frame with a softer outer layer molded around it.
An investment in such a thing on Purism’s part would be a great thing for their customers, and likely cut down on need for replacement parts like screens and housings.