You can make money out of Public domain characters because nobody owns them anymore. That is why we have a Winnie the Pooh Horror movie right now.
So how can you take advantage of a Public domain character?
1.Make your own interpretation. The Wizard of Oz is a Public domain story so you already can write about the lore of that Universe. Nobody will sue you for writing a novel about Dorothy Gale and characters of your story as long as she doesn't wear Ruby slippers (Warner Bros copyrighted the Ruby Slippers, Dorothy Wear Silver Slippers in the book)
Winnie Holzman is a writer who decided to make a story about the Wicked Witch from Wizard of OZ and portray her in a sympathetic light. That book is wicked and it got adapted into a broadway Musical that made billion of dollars.

It will be adapted into a movie soon. It is hard to make your own characters but writing fan fiction with established Public domain characters is easier because people know their personality. It is easier to use them than make your own characters and start from scratch. You can make your own version of Snow White, Peter Pan and Robinhood and it won't be an issue at all. The descendants of their authors may not even know they are related to the author. They have no more copyright owners.
If you want to write your own novel but you are not yet capable of making your own characters, Use the 100% Public domain character. Just remember if you will use a Public domain character it should be your own version. You cannot use Disney's version of Snow White or Aladdin. You have to make your own version and art style.
Also you can even copyright your own version of a copyrighted character. Like your own version of let's say Cinderella have her own last name. With that No can pirate your version of her. The Wicked Witch from OZ have no name but the author of Wicked gave her a name, Elphaba so no one can steal his version of her.
2. Use them as Mascot for your business
Once a character is Public domain, You can take advantage of their image or even just their name. A logo or a mascot or name can be helpful to market your business. These names and characters are household names. They are free for you to use so why not take advantage of them. People have nostalgia from these characters so the familiarity makes an instant market.



3. You can republish the source material. The novel Dracula is Public domain,That means you can republish the original material or translate it in other languages and sell those copies and have no issues about legalities. Some Publishing companies made money out of Public domain novels with no issue.










