Injection molding comes in several different varieties,but can basically be described as forcing liquid plastic into a metal mold under high pressure. Most injection molding is done with high temperature molten plastic, and then it quickly cools inside the mold. The part is taken out of the mold, and then the process is repeated. The benefit of this technology is that thousands or millions of components can be made very quickly, and inexpensively. The downside of this technology is that the mold is usually costly. (lots of variables here- design life of mold, cycle time, etc) Usually you would use this technology to make thousands, or tens of thousands of parts- this makes the cost of the mold very small on a per part basis.
There is another technology called RIM (reaction injection molding). These molds are less costly than the other, and in this process, cool liquid plastic is injected into the mold, where it sets up chemically. (like epoxy or fiberglass, only a polymer plastic)
To begin along either one of these paths, you need to start with a product that is designed with molding in mind as the production process. There are many product details that may make a part easy or difficult to mold.
If you have a basic product concept or design, then you need someone to develop it into a full 3D CAD model. I have attached an example CAD model for you to see.
Beyond this point, the costs and direction you should take will vary widely, depending on the size and nature of your product.
GI Engineering Co.
I was browsing previous comments, and thought I would give my 2 cents.
If there is really interest or demand for significant quantities of molds, I can help with developing an injection mold and producing plastic versions of the fiberglass molds.
There are various high strength polymers available, but I bet we could produce mold sets for under $10 per set. We would have the capability of producing them in the hundreds or thousands or tens of thousands. High quantities would be even less expensive.
For comparison, think of the 5 gallon plastic buckets and plastic lawn chairs available. The manufacturing process is the same, and the equipment is readily available where I live.