Open-side containers are difficult to ship for one structural reason: they rarely appear in depot surplus, so there is usually no positioned unit near you to buy. Almost every one of them starts as a factory build, and moving a small batch of factory builds across an ocean is what makes delivery the hard part rather than the price.
Depot stock is what carriers leave behind when they reposition equipment, and carriers reposition standard dry containers. Door Units are built for specific shippers with specific loading problems, are owned by those shippers, and usually stay in service with them.
So Door Units rarely appear in depot surplus, and local availability varies by market; a factory order is the reliable route for a defined batch. The depot stock page lists 40HCs for exactly this reason.
A side-door unit is still an ISO box on the outside, so it stows normally. What changes is the handling of a small quantity of shipper-owned special equipment moving on a one-off basis: it needs a booking of its own, it is not interchangeable with carrier equipment, and it does not benefit from the volume arrangements that make standard boxes cheap to move.
That is why an empty repositioning quote for a handful of open-side units usually looks unreasonable against the value of the units themselves.
The workable route is a first trip: the new units are loaded with export cargo already heading toward your region, so the ocean leg is paid by the cargo and the containers arrive as your property after one voyage. It is usually the practical way a small batch of purpose-built containers crosses an ocean at a sensible cost.
The schedule follows cargo availability on your lane rather than the production calendar alone, so the quotation states a realistic window rather than a fixed date.
Decide the door configuration first, because it drives everything after it. A 20ft unit carries two separate double-door side openings and a 40HC carries four, with wall and frame structure between them, so what you get is several separate openings rather than one continuous opening along the side. Clear opening sizes are on the 20FT Open-Side and 40HC Open-Side pages.
Then plan the lane and the window before the deposit rather than after it.