Related question: Just how many Starships do you think will be necessary to fulfill all our launch demands? Given that it's designed to be reusable and it has a huge payload capacity, perhaps there is less need to mass-produce them, since fewer vehicles will be able to do the same job as many expendable vehicles...?
Note that the killer feature of Starship, IMHO, is in-space refueling. This isn't a Earth-based heavy-life vehicle... it's a re-configurable spaceship able to explore the entire solar system through fuel depot staging (with Starships themselves serving as both tankers and fuel stations).
“I think there is a world market for maybe five computers.” -- Thomas Watson, chairman of IBM, 1943.
Then there is the idea of using Starships for very fast transport on earth. Fly from NYC to Sydney in half an hour. If that catches on, they may be replacing part of the airplane fleet.
Then there is lunar shuttle services, satellite transports and asteroid mining.
My guess is: a lot.