It probably isn't though. My mother in law's stairlift was installed in a couple of hours along the normal stairs. There was no building work to create a shaft needed. It was cheap.
This is key - they didn't have to do construction and make a shaft with the chairlift. That'll put the prices up.
Reengineer this mechanism to run along inclined rails.
If cantilevering from rails on one side is impractical, make it detach from the opposite rail at the top/bottom and swing out of the way.
The requirements for space (a column of free area 80cm by 80cm) are so small that I don't even think they make elevators that small.
You don't have 80cm between normal floor joists so installation in a regular house could be complex and expensive. If you are designing a multistory new build specifically for the elderly leaving a space for a solution like this to be installed/uninstalled in the future could be added to building standards.
sure, I'm just saying that a elevator normally takes up much more space and is therefore more expensive to start with.