Good idea, but I see ads in that sector saying "Molds start at $4990".
I've seen people do things like this at TechShop. They carve a positive mold out of maybe a dense wood. Then use that to make an negative mold out of some pourable plastic like RTV. Then insert the device, pour in epoxy, and wait for it to cure. The negative molds wear out fast, but you can make more from the positives. There are lots of plastic options and books on this stuff. People use these processes to turn out stuff to sell on Etsy. All this is do-able, but usually messy.
Still, struggling through the process to have an MVP to show resellers is worth the trouble. If you get a big order, you can go out to Cavist or someone like them and have them produce in volume.