a ladder or a flight of stair
Flight of stairs and Fleet of ships.
A flight of stairs in it's entirety is a staircase
stair and stare
Stares and stairs or Stare and stair
Generally, a stair lift can be installed professionally for about $3500 for a standard lift, on a straight set of stairs and only a single flight. Turns and non-standard stair configuration will increase the price substantially.
A hand truck with a stair climber built in.
It is one word "staircase" (open flight of stairs, usually with rails).
The company Bruno makes many different types of stair lifts. Bruno's has outdoor stair lifts, straight rail stair lifts, custom curved rail stair lefts.