I have not experimented with anything less than 1/2-inch plywood. I really like this thickness for public installations etc. That said, I always -- and very quickly -- cut the 8'x4' sheet down to 8" sq tiles. These pack very nicely, though I understand are difficult to move when large quantities are involved. Since there is 1/4" finished plywood easily available, I suspect you could achieve pretty good results with these, and double your quantity to weight ratio.

All that said, since I am loath to travel much out of my day job, should you or any of your allies make it to Vermont I will be more than happy to go out of my way to make it worth your while!