[froj]

For injection molded parts you could start by paying a local consulting firm that specializes in mechanical design to take a look at your part. They will probably be able to help you find a manufacturer and your design will have to be verified by somebody who does this for a living one way or another if you want it to work after a reasonable amount of iterations (better not forget those draft angles). You could also directly ask a local manufacturer of injected parts, as they will have engineers that can help you, but they might only want big customers. Also, that might close doors if you want to move production overseas.

Depending on the size and complexity of your part might just make it for $15k to get the tooling done. The manufacturing itself most probably will never make sense to do inhouse.