Back in my Motorsports days we built many many fiberglass, Carbon Fiber, and Kevlar body parts for road race cars. It is all about the moulds. Building these from dimensions is not the way to do it. If I were to do this I would start from a very clean set of doors and build the moulds then start to produce the doors from there. The moulds take up a lot of space (they are built with a lot of wood, metal, resin etc to stay stiff and hold shape) and the doors are large and also take up space. To be efficient you would want to make a lot of doors over weeks and weeks vs one by one. So in the end you need 1000 sq/ft to just store the moulds, doors, raw materials, etc. Then there is still the metal slider mechanisms, lock knobs, inner and outer handles, hinges, glass, paint, seals. For $1500 a set I would lose money and at say $2000 it would take hundreds of sets to make anything from this project. I am not saying no but when another vendor sells them for $5K I would not say they are gouging, I would say they have invested a lot and they are looking to make a return. That is capitalism, and if that vendor sells enough sets to make a profit then good on them. That will support them making more products for these trucks and keeping them going.