Just an estimate but I think this key in steel would be less than $50 on shapeways.

EDIT: I just uploaded the model to shapeways to get a quote and this key is:

    $26 for steel
    $44 for aluminum
    $75 for brass

The brass would probably have the most dimensional accuracy.

I have a small company that sells custom jewelry, and some of my customers want steel rings. They usually cost me around $15.

On possible downside is that due to cooling shrinkage steel only has about 5% tolerance. This can be accounted for in the 3D model. What I usually do for jewelry is order the ring in 2 or 3 different sizes and then choose the one that fits best. In terms of this key, I am not sure how much 5% error would affect its functioning.

Just sent my model to a popular 3d printing service for around $80. I've used this key daily for almost 3 years and never had any issues.

Depends on your need. For a key you'll only need/want to use one or two times, plastic will be able to hold up just fine. If you need something more durable, there are a number of 3d printing services that'll print whatever you want in metal without any questions asked. Desktop sintering printers are also getting cheaper and cheaper. They're still several thousand dollars, but that price will only come down now that patents are expiring and people are starting to be able to work on the processes to get them more resonable in cost.

You can probably find a desktop CNC that can cut a key based on output from OpenSCAD. Maybe a little tweaking required, like plotting difference() of a cube that encases the key model.

The key doesn't need to be strong, not even strong enough to turn the lock. The key only needs to get the pins to align. After that you can use a metal turning tool to actually rotate everything. A bent wire would do.

Wouldn't a CNC mill (or even a manually controlled milling machine) be a better tool for fabricating keys? Brass is pretty easy to machine.

ABS and PLA probably would be too soft but some locksmiths use soft material with a skill call impressioning.

Most modern home FDM printers can reach temperatures high enough to print with poly carbonate which would work fine as a key. PolyC is prone to warping but on such a thin print I doubt warping would be an issue.

I’ve used plastic for 3D printed pin tumbler and disc detainer keys. It works well enough as a proof of concept, though not something you’d want to rely on for daily use.

You can encase it in a plaster mould and use lost wax casting to get a metal key. A bit more involved in terms of time and money, but not prohibitively so.

you don't need to make it that complicated. if you are determined enough and have a little practice you can make alot of shapes with just a piece of metal and a file.

PETG might work.