A short mystery story by acclaimed playwright Tom Stoppard raised $7,892.
Rowling was able to squeeze her Harry Potter prequel onto both sides of a piece of A5 paper, which is slightly bigger than a postcard.
The prequel to the seven-book series, which goes online Wednesday, does not offer hope for a new Potter novel. Rowling finished her card by writing, "From the prequel I am not working on - but that was fun!"
Twelve other authors and illustrators also contributed cards to the auction, including Nobel Prize winner Doris Lessing, and fellow British novelists Nick Hornby and Margaret Atwood.
Copies of all the cards will be on display in Waterstone's stores and online following the auction, and they will be collected into a book available in August.
The final installment of the seven-book series, "Harry Potter and the Deathly Hallows," was published last year.
Rowling has said she has no plans to write another novel about the boy wizard, but in December she sold a handwritten, leather-bound book of fairy tales she described as drawing on the series' themes for nearly $4 million at an auction. The money went to The Children's Voice, a charity Rowling co-founded in 2005.
