Well, I use real sand from TRU sometimes for some dioramas, like Tatooine stuff.
For my Geonosis battle scene, I purchased some red sand off the internet, it wasn't cheap but it was well worth it.
For snow effects, I prefer to use caulking (like stuff you put on walls) and let it dry, then paint it white.
Then for mountains and stuff, each one of those cost around $15.00 if my memory serves me right.
Also, check out a hobby store for mossy looking shrubbery plants. They work out really well for wooded areas like Endor.