"I use cleaned and dried sand from a pet store, usually used in fish tanks. if you prefer crushed rock, they have that too. lead is dead as they say, if it’s not encapsulated don't use it."
To elaborate on this, I would go with epoxy coated #2-3 aquarium gravel any color you want. It's clean, dust free, can be purchased in a number of pre-packaged quantities, is probably more economical and as good as anything anyone else has mentioned in this thread.

