There are a number of items that a customer has to consider to justify tooling dollars. Since mold building ( actually technical sales) is how I make a living, I can speak volumes to tooling costs.
When it comes to the screw on retainers that Estes offers, they could justify a tooling cost as they not only develop there new rockets around them ( all pro series are 29mm) they also saw a market place outside of just there rockets that could use them. Every new rocket they release helps that Capital investment further pay for itself. Based on that success is why they added 24mm. Again they make a number of kits with 24mm mounts and they can fit on other kits produced by other manufactures.
While I assume they had tooling built in China for these, I can guarantee you the cost for both molds was nowhere near $10,000.00. The cap has to have an unscrewing core in it to remove part from core. The notches on bottom of cap keep the part from spinning in the mold. Part is thick-walled and more than likely a multi cavity to get piece price down as low as they are. The part that goes on motor mount requires a mold that has 2 side actions plus the main open and close of mold and again probably a mutti cavity mold to drive piece price lower.
I don't think they are using PVC as the material based on cost of parts and PVC resin when it is being injection molded would break down the tool quickly due to the corrosive gases in it during molding process.
If the threaded cap was a 2 cavity mold , I would bet average china price is $15,000 to $18,000 a tool built in US would be $25,000.00 to $35,000.00 depending on option included in mold.
If the part we put on motor mount tube was a 2 cavity tool , China price is probably $12,000 to $14,000 a US tool would be $22,000.00 to $28,000.00 again depending on options.
That just gets you the molds to make parts, now you have to mold parts - which means resin costs, press rates, and operator rates, packaging, and quality control costs all need to be factored in. If I was to guess Estes probably has an EAU of less than 100,000 units so that has to be factored in to your justification cost model.
Based on that I doubt you will see 38mm options offered by anyone unless Estes decides to produce 38mm kits, which if John is reading I would welcome.
