[vlehto]

"The cost is much higher than a mass production case (likely 50-200+ times more expensive)"

Mass production case has two advantages. Big batch size and insignificant cost of design/product. For the CAD-work I would pick someone I can meet personally and often. After that, if you pick plastic, you have multitude of options how to produce the prototype. However it's "only" hundreds of dollars now. Casting, CNC and 3D printing are all competitive options for crude model.

For refined piece like the example, i'd seriously consider making aluminum permanent mold for a casting run. It's good for production run of few thousand products, while CNC milling aluminum mold is not very expensive. You have to spend bit more time in design phase, because now you have to think how the finished piece exits the mold, etc. But the good thing is that this is identical to the mass production tools you are eventually going to order. The only differences are the hardened tool steel as material and possibly Electric discharge machining replacing CNC.