Yes, I think it is three shillings and six pence.
The story is from a collection of short stories by British writer Rebert Aickman (1914 - 1981), a search on Google shows.
There were 20 shillings in a pound (£), and twelve pence in a shilling.
I looked up a relative comparison site for historical currency, and the answer is, "In 2014, the relative value of 3s 6d from 1960 ranges from £3.36 to £11.99 (on a purchasing power basis)."
It would have been so much more interesting for us, and helpful, if Cloud had given the names of the story, the book and the writer, as well as the fuller context. Who paid three and six for what in which city during which historical period?
Next time Cloud will give all the relevant information, so that all of us will do a better job and enjoy the process even more.