Sounds like you have a good experiment. Buy a small amount of sand and project onto it.
During my early prototype, I used the 35lbs or so of tan/gray sand we had in stock and it looked fine. As long as your projector is bright, I would expect any light tone sand to work.
I did end up buying the Sandtastik White sand. Out district’s office supply vendor happened to sell Sandtastik sand and that saved me the price of shipping 200lbs of sand.