I build my trailers to suit my myself. What they do not come with are butter and guns, water, bedding and clothes.
If there are components that you do not need right off, they can be subtracted and picked up at a later time. If you already have a generator, or solar, then you don't to spend $486.00 for the Zamp Solar system. If you don't want the vestibule and footprint right away, subtract some more. If you don't need a gray water tank that will save you some more. If you have your own tires and rims, bring them and cut the price a little more.
Another way that I keep the cost down is by producing as much in house as possible. We have 12 sewing machines, sheet metal and fabrication abilities and we also assemble our own 12 Volt LED lamps and include these items and others, such as the battery box, at a wholesale price - complete package deal. We paint our trailers in house with color matching no extra charge if the customer has the paint code.
What I cannot compromise on cost is with the honey-comb aluminum panels that make up the floor, side walls of the box and the top deck/sleeping platforms. The floor weighs about 25% of a typical plywood floor.
Mitch Schliebs