Ownership rights for ebooks will still ensure that supply and demand forces will be at play and equilibrium has a role.
When J K Rowling writes a new book, that takes time. As an author, she does not have "unlimited" supply and will want to make a return on her efforts to write the book. Therefore she will look to sell the book through an online 'store' such as Amazon, for example, and there will be a price associated with it. It will also be up to the consumers as to how much they want to read this book, and their demand will therefore play a role. Just because you can distribute the material via electronic means almost without limit, does not mean you are able to do so. Copyright laws still exist to prevent such free sharing.