It’s definitely cheaper to stay on the US side of the falls. If you want to save money, you can stay on the US side and drive over into Canada during the day, where you will find lots more activities than on the US side.
Just know that border crossings do take a while, and they close at night, so give yourself plenty of time to get there and back.
Buffalo, NY, is only about a 20-minute drive from the falls. There’s plenty to do there as well, so you might consider that as your home base.