WTF, slashdot ate the top paragraph, sorry, let me try that again.
If a program can be sufficiently complex so as to create the program for the 3d printer to print the key with less than 5 dollars of effort, they could just as easily create tool paths for a CNC mill.
If you have to create the 3d printer program, well that's not any easier than creating the CAD drawing for the CNC machine. I can build a CNC mini-mill for 1500 dollars, so they are cost competitive (in relation to this topic) with the 3d printers also. Side bonus: steel key is much more resilient than plastic.
The world is moving so fast these days that the man who says it can't be done is generally interrupted by someone doing it. -- E. Hubbard