Maya, like a couple of other high end 3D modeling/animation packages cost several thousand. The last time I saw the cost of 3D Studio Max it was about 6k. There are learning editions though, which are very powerful, but usually add a watermark to renders and limit the size of those renders. They also forbid you to use those renders for commercial use.
Its a very VERY good model, most people don't bother with dirt when they model and render cars, but I think its worked really well with this model.
As for the scale issues I not too sure. Have a look at some pics on
this page. People who model things in that kind of detail tend to spend the majority of the time looking at blueprints, but more so, reference pics and sometimes even scale models (dinky cars, etc), so any inaccuracies are usually just tiny things that even the most anal of people wouldn't spot!

Also, this has been done for ages, I remember seeing this when I first got into 3D modeling, all those years ago....