Sixpence

Sixpence was a unit of currency used in the United Kingdom.

Before World War II, sixpence coins were either made entirely of silver or at least contained some silver, however after the war they were instead made of cupronickel. (PROSE: All I Want for Christmas)

The Twelfth Doctor, accompanied by Bill Potts, paid sixpence to a waterman to enter the 1814 frost fair. (TV: Thin Ice)

The Tenth Doctor claimed to Queen Victoria that Rose Tyler was a feral child who he had purchased for sixpence in old London Town. (TV: Tooth and Claw)

During the London Event, Gwynfor Evans asked Jamie McCrimmon if he had a sixpence to purchase a bar of Camfield's Fairy Milk Chocolate from a vending machine they had found. Though Jamie responded in the negative, Evans tried the machine without inserting any money and discovered, to his surprise, there was a chocolate bar in the machine's open compartment. (TV: The Web of Fear)

Behind the scenes
As promoted in the Walls' Sky Ray lollies advertisement, sixpence (6d) was the price of a Sky Ray lolly.