This is good. We went to the dollar store and got a bunch of different smooth glass pieces. We also went to Wal-Mart and got several bags of stones and one bag of shells.
We also got a couple bags of small gravel from the aquarium section.
I got home and had a tree mail from Bubbles offering to send me a box of glass (thank you - I replied!).
So, I think we're pretty established here.
I haven't fully measured yet but I estimate it'll take around 50 stones total. They stones will be hexagons and about 9" wide.
Here's a picture of our stones purchases:
