According to some older guides and Internet reviews, access to the Daredevil Gallery is free, but it seems that since the renovation work was done in 2009-2010, there is now an admission fee of nearly $10/adult (after taxes).
While seeing and touching the barrels used by the daredevils (and reading their history) was interesting, I cannot see how anyone could spend more than 20 to 30 minutes in this relatively small exhibit. I won't go so far as to say that this place was a tourist trap, but I do consider it overpriced.
I would recommend buying a combined ticket called the SkyMax Combo that includes, along with entry to the Daredevil Gallery, a viewing of an IMAX movie about the history of the Niagara Falls (the Daredevil Gallery is located inside the pyramid-shaped IMAX Theatre) and access to the nearby Skylon Tower observation level. Basically, it comes to seeing the movie or going up the tower for free.
The address of the IMAX Theatre and Daredevil Gallery is:
6170 Fallsview Boulevard, Niagara Falls, Ontario L2G 7T8.