I don't believe you ever have to pay to view it. If I remember correctly the $50 fee is to regrade something officially.
The Math Dept at Mac has official viewing procedures outlined here:
http://www.math.mcmaster.ca/index.ph...view-info.html
If you're looking to view an exam in another department, I would start by emailing the prof, and if you don't hear back, contact the administrative team for that department about the procedures they follow.