The Harry Potter author, whose new book The Casual Vacancy was released last week, told fans that the trip had been offered for the cost of £2 million ($1.24m).
Speaking at an event at London's Southbank Centre, Rowling said: "I was offered a seat. For a mere £2 million I could have been on the shuttle, but I turned it down."
Rowling recently admitted she is tempted by the thought of writing a 'director's cut' version of the Harry Potter novels, allowing her more time to improve on the original seven books.
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