A few comments on tooling cost:
For something like a 400E type loco, there are a lot of tools for stamping and forming, and for die casting. These can be very costly. But it is designed for high production, I'll bet there are thousands of MTH 400E's out there.
I am moving to water jet cutting of sheet metal, but we are still talking flat and not formed - that gets much more difficult. The McCoy, CMT and Forney cars are examples of low cost tooling. I have used it for the Daylight mechanism frames, super accurate and great finishing.
For castings, if you can go sand casting, it's all about a pattern, which can be made of wood or metal, and can be hand formed. Castings are much rougher than die cast, but cost of tooling is significantly less than a die cast tool set. A trade off. The Lee Lines and Harmon locos and cars I make use simple sheet metal and sand castings. And an occasional resin cast plastic part, which also starts with a pattern and a silicon mold, cheap and good for low volumes.
3D printing enables cheap one off trains (like my PRR K4), or low cost patterns for sand casting (which I will do eventually). You just need a good 3D CAD model, and there are some good young designers out there doing wonderful work (see Shapeways). But tinplate guys don't like plastic!
What I find hard to find are good motors and gears that will hold up and provide the pulling power.
So bottom line, if you are making short runs like Harmon, Roberts Lines, CMT and others have done (and Dave Carse is doing now with CMT), there are low cost tooling processes (less than $10K), enabling pretty nice unique end items. If you want something like the 400E, or like the Lionel Hiawatha set of the early 2000's, you are talking a quarter of a million $ for the whole tool string, which requires 500 or more units to justify.
Jim Waterman