Image via ptiprototype

A main barrier to entry in developing new products is often the high cost of injection molding. The initial tooling fees mean that prototyping is reeaaaalllly expensive. From core77′s blog post on the inexpensive alternative, spin casting:

Injection molding is awesome. It’s also freaking expensive, with high tooling costs that keep it out of reach for your average independent designer, craftsperson or hobbyist. For those seeking to create smaller runs of smaller objects, the production method known as spin casting provides similar capability at a fraction of the cost.

To dumb it down a bit for the non-production-method-initiated, injection molding requires the mold—typically made from steel—be precision-machined, which is where the high cost comes in; obviously it depends on the size of what you’re molding, but generally speaking you’ll pay anywhere from high four to low six figures. Manufacturers offset these costs by producing high runs.