I always use catlitter and ordinary sand in dio``s same with small pebbles.
Sand you can find anywhere and I always have different types of sand available at home.
We have two cats so the kitty litter is nt a problem too but always the cheap stuff works the best and looks the finest.
small pebbles.. Sure you can invest too much money for a small bag of pebbles at the minirailroadshop but for the same amount of money you can buy 15 kilo`s of small rocks and pebbles at the aquarium store (that`s enough for the rest of your life)
these are just a couple fo guesses for cheap groundwork stuff that always looks the best