No, it’s always free to enter Niagara Falls State Park. You can see the falls from there, and it’s open every day of the year. As the website explains, the park “also features thrilling attractions, interactive exhibits, miles of hiking trails, and delectable dining options in a family-friendly environment.”
Moreover, “No passport is needed to experience an unforgettable and breathtaking Niagara Falls vacation.” If a passport is an untenable expense, or you simply don’t want to deal with it, you can still have a Niagara Falls adventure.