If you're not making thousands of parts, injection molding is the wrong manufacturing method.
You might be able to buy an injection molding machine for pretty cheap, but it's useless without the appropriate tooling which costs a fortune, and the learning curve for operating an injection molding machine is very steep. If you don't have the equipment and skill to machine your own tooling then trial and error is going to be real expensive - I'd definitely invest there before trying injection molding yourself.
I would recommend calling up a chinese injection molding shop and having them run your parts instead - they have the experience and volume to produce tooling quickly and (comparatively) cheaply, and that's all you really have to pay for. You could always go through the trouble and expense of producing things domestically after you've validated your design. The one downside is that they'll usually just make your design as is, whereas a domestic shop will usually assist you with some design for manufacturing to make sure you get something that actually works for you, but the cost is so high its still often better to screw up a few times with the chinese shops, and nowadays some of them are better with their customer service anyways.
But for short runs you really should consider alternatives. The appropriate one depends on what you're making. Urethane casting is great for making plastic parts with tolerances comparable to injection molded parts - you can even use 3D printing to make the master molds. CNC machining is also very economical for short runs.
You might be able to buy an injection molding machine for pretty cheap, but it's useless without the appropriate tooling which costs a fortune, and the learning curve for operating an injection molding machine is very steep. If you don't have the equipment and skill to machine your own tooling then trial and error is going to be real expensive - I'd definitely invest there before trying injection molding yourself.
I would recommend calling up a chinese injection molding shop and having them run your parts instead - they have the experience and volume to produce tooling quickly and (comparatively) cheaply, and that's all you really have to pay for. You could always go through the trouble and expense of producing things domestically after you've validated your design. The one downside is that they'll usually just make your design as is, whereas a domestic shop will usually assist you with some design for manufacturing to make sure you get something that actually works for you, but the cost is so high its still often better to screw up a few times with the chinese shops, and nowadays some of them are better with their customer service anyways.
But for short runs you really should consider alternatives. The appropriate one depends on what you're making. Urethane casting is great for making plastic parts with tolerances comparable to injection molded parts - you can even use 3D printing to make the master molds. CNC machining is also very economical for short runs.