If you’d like to gain the rights to stop someone who is infringing your rights, I recommend that you actually have a legitimate copyright that's registered with the U.S. Copyright Office.
This will give you the rights to ensure that others don't infringe on your natural rights as the owner of the work. This empowers you in a court of law to have a greater chance to get what you deserve for your work.
Fees charged by the government for a registration may change each year, and depend on the character of your intended enrollment, but typically run between $50 and $100. As of the time of this writing (in April of 2021), fees are $35 for a single work, and $55 for multiple works (up to 10).
However, copyrighting your work yourself EFFECTIVELY can be a difficult task. If you plan to make a living through your copyrighted work, we’d recommend talking to an attorney FIRST. That way, you don’t accidentally miss out on any rights you could have given yourself.