A sketch which inspired the cover of Jk Rowling's Harry Potter AND THE PRISONER OF AZKABAN is being sold for GBP8,500 ($16,575) at a London art fair. Despite the high price tag, fans of the boy wizard franchise could snap up a bargain as experts predict the pencil drawing of Potter and his friend HERMIONE GRANGER on a hippogriff (lion/eagle cross) could reach double that at a future auction. Illustrator CLIFF WRIGHT, who also designed the cover for the second fantasy book HARRY POTTER AND THE CHAMBER OF SECRETS, created the picture in 1999. He says, "In some ways I prefer the sketch to what ended up on the cover. It's more dynamic: in the final version, the hippogriff is not moving quite so fast. "JK Rowling herself faxed over an image of what she thought the hippogriff should look like."