Look in my locker under "Leather replacement project" and you'll see that I had the seats out and then into a hundred pieces too.
I was able to lift them up and out of the car, up a flight of stairs to my apartment at the time, etc, so I know they aren't 200 lbs (wish I was that strong though
). Next time I have them out I will weigh them just for reference though, maybe 40-50 is a bit light. Todd's spreadsheet sounds like a great idea.