To determine the kind of tooling needed to make your plastic part, you should know the estimated annual usage or EAU. Most parts that have an annual usage of more than 10,000 for simple geometry and 50,000+ or more on complex geometry are feasible. Just to clarify, some parts are produced in the millions yearly by plastic injection molding while some highly specialized parts that can only be injection molded may be produced in very small lot sizes.
EAU of 100,000+ are normal in the custom injection molding business range of 50-250 ton press capacities, but are not a prerequisite. A well-maintained plastic injection mold can continue to produce consistently accurate parts well beyond 10 years. Extremely intricate parts can be produced in mass at a low cost with a properly constructed mold. Some high wear materials such as glass fiber reinforced plastic may require hardened tool steel inserts.