Basically all you save on using a shipping container versus a regular tiny home is the cost of some shell framing, minus the cost of container, delivery and rigging expense.
You will find that most containers are (surprise!) for sale near ports and depots, not in the middle of nowhere.
They can be found inland, but are generally more abundant and cheaper where they get used.
After you buy one in decent shape, you have to pay to have it delivered and any rigging.
That can range from crane rigging to a big forklift onsite to lift it.
Then you need to consider foundation.
Will it be on some sort of platform, footing or just on dirt or gravel?
I've seen many containers set down for temporary storage on what was level land, that later sank into soft ground or ended up tilting due to runoff/erosion.
Next you have to deal with unconventional construction to finish the interior.
You don't want to put holes all over the container to attach utilities and interior systems.
Where do you attach electrical boxes, wiring, piping, conduit, etc.?
So you need to decide if you will stud/fir the walls out somehow.
Don't forget about insulation. Those are bare metal walls, it will be an ice box in winter and an oven in summer.
you can mitigate this to some degree buy partially buying the container, but that also has issues with moisture, rust, etc.
You also need to consider openings in walls. It's unlikely you will want to swing open a 4' wide end door the full height of the box, letting out all of your comfy cool/warm interior air every time you enter exit. Unless you like living in a coffin, you'll probably want windows and/or skylights. These openings have to be cut into the steel framed some how to support hinges/hardware and accept standard construction windows, doors and skylights.
It is tempting to think of containers as "instant houses" but in reality they pose some challenges and may not offer much benefit over traditional construction.