Is there an entrance fee for Niagara Falls?

No, there is no entrance fee to see Niagara Falls itself. The falls are in public parks on both the U.S. and Canadian sides, and you can walk right up to the railings for free. On the New York side, Niagara Falls State Park is free to enter, but you'll pay for parking (around $10-$15 per car at the main lots). On the Canadian side, Queen Victoria Park is also free, but expect to pay for parking in lots or garages, usually $20-$30 CAD for the day.

If you want to actually get on or near the water, that's where the costs kick in. The Maid of the Mist boat tour (U.S. side) is about $25 per adult, and the Hornblower cruise (Canada side) is around $30 CAD. Both are worth it if you don't mind getting soaked. Cave of the Winds on the U.S. side (about $20) lets you walk right next to the Bridal Veil Falls, and the Journey Behind the Falls on the Canadian side (about $20 CAD) is solid. Skip the overpriced observation towers and the "4D" theater shows unless you really want the t-shirt.