Have you seen one, or a sample? Do you know the level of detail on it or the complexity involved in the underframe, tank and mounting system?
You seem to suggest that just because the wagon has a flat base for the tank to sit on, there will be very little detail involved. The pictures that have been shown, including on this forum, seem to show, at least to me, lots of attention to detail.
Let's not forget the cost has to include everything, not just 'super detail', but research, design, packaging, production, manufacturing, marketing, shipping, retailer margins etc etc.