A cost that nobody seems to have factored in, is removal and disposal of
the oldwaterheater.

Cost? I get money for the old units at the recycler, it's an insignificant
amount, but probably enough to cover the fuel spent getting it there.

Somewhere I saw the cost as 10 dollars at Home Depot for removal of
the old heater.
That's of course if you pay the 400 dollars for installation in the
first place.
Otherwise, the cost is to leave it outside for a week until someone
with a pickup takes it to the recyclers for you.