How do commercial companies design and produce models? And how much money is needed?

3d cad models to machine the dies, that then still need cleaned up by trained tool & die makers. (Big hunks of precesion machined Steel) Injection molding machnes to produce them. It's easily in the tens if not hundreds of thousands of dollars!!

So basicaly a CAD software is needed to make the die/form, then the die/form has to be refined by the expert, and then the plastic get's inkjected into it and the model parts come out, right?

On Trumpeter's site a while ago I noticed that they had screenshots of their models in 3d. I thought that the screenshots were from the CAD software that they use. I did some research and found out that SolidWorks software is one of the most popular ones.

some companies will outsource for their "masters"also. I know Tamiya,Verlinden,jaguar have all done this in the past..its a respectable way of doing business..

So how much would something like this cost? If the design is ready.

around $2000.00 USD for a relatively simple diorama base

Are you wanting to do it in Plastic or Resin... the cost of doing it in Resin is a lot less. You can get the moulds (silicone rubber) and casts done for hundreds, not thousands of dollars.