So I ordered a sheet of the durable and less expensive material off eBay from Seymour Solar. It was cheap and they even threw in a free pair of paper goggles with the film installed. Win! Also, I've heard you can get this material from your local photography & telescope stores in a pinch.
With a sheet of poster board from walmart, xacto knife, scissor to cut the film and a hot glue gun, I was able to throw this little ugly duckling together.
*After I took these photos I managed to clean up the edges considerably and I'll be adding a little something just to make sure it doesn't blow off the scope and burn a hole through my head. Updates forthcoming.
Trace and cut two rings that match the size of the scope, such that they'll rest on the face of the thing. I was liberal with the size here to help prevent light from leaking in. Then I made one (you could, of course, do more) outer right that fit around the outside of the scope. This works as a lip to keep the thing in place.
Checked the ring sizes before I went any further, everything was close enough. Then I cut the film to match the outside diameter of the rings, and glued it all together. The two smaller rings hold the film in place while the larger one gives it a ring to sit on the scope.
I ended up cleaning the outside with the sanding bit on a dremel, which gave me nice smooth edges. These photos are of the unfinished edges. Last minute fix will be to add clips or a shroud to make it hang on a little better. A good gust of wind could take this cap away. That'd be pretty awful when you're looking at the sun.
"I'm making a note here... huge success."
Things went really well and folks got a look at something that won't happen again for 100+ years. I'm happy!