Ticket of the knight bus, done with my own design on a very light paper, pretty close to a sales receipt as glimpsed in the 3th movie, "The Prisoner of Azkaban" (we can barely see a white ticket from the back)

Is available in the two main route used in the books by harry or Ron or Hermione:

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Little Whinging to London
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The first route took by Harry in the 3th book, when he ran out the house of his uncles. The price of this ticket is very well known, 11 Sickles.

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Islington to Hogwarts
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Islington is where Grimmauld place is, Harry, Ron and Hermione used the knightbus on the 5° book (the order of fenix)  to travel back to Hogwarts after Christmas Holidays.
I calcuated the price on the basis of a pretty deep research of a fan published online where he calculate (narrowly) the miles from london to hogwarts.