The cost of signed novels can vary widely. It could be just a few dollars more than the regular price if it's a relatively unknown author. For example, a new self - published author's signed novel might be only $5 - $10 more than the unsigned version.
If it's a well - known and highly sought - after author, the price can be significantly higher. A signed first edition of a classic novel by a famous author like J.K. Rowling could cost hundreds or even thousands of dollars. The price also depends on the condition of the book, the rarity of the signature, and the popularity of the title at the time of sale.
At auctions, signed novels can reach extremely high prices. Some rare signed copies of important literary works have sold for tens of thousands of dollars. However, in general, you can expect to pay anywhere from a small markup to a large premium depending on all the factors mentioned above. And sometimes, at a local used bookstore, you might find a signed novel at a very reasonable price if you're lucky.