If you are not absolutely set on steel, you can design something small and pay about 50 bucks on shapeways. But that will be SMALL. I tried something of the kind and I noticed something : you need to really know what you're doing to hit the right frequencies, and actually hear something, even more so to get a pleasing sound.

What I mean is that : with today's sintering, the metal is porous and you need something over a mm thick to have a chance it gets out ok. So good luck.

What would make more sense is you make something in wax and cast it. Requires some hardware and knowledge...