The LHB Dart stock, despite its apparently simple shape, presents a fair degree of challenge. Will you try to produce a ready-to-go model, or break it down into kit form for us to assemble? How will the moulding be done, e.g. 3D printing or traditional expensive injection moulding? Will you cater only for 00/16.5 gauge, or will there be allowance for 21mm people like me? There are costs incurred at every stage.
And people do expect to see inside the models, so windows must be transparent, which means getting your frames right, plus a representation of the seats and sliding doors.
As you're discovering, the whole thing's not as easy as it looks!