If only anubias are going to be planted, I'd agree with rex and others about the shallow layer. Which is too bad, as a deeper layer creates more stability in the tank . . . . maybe about 2" and get some malaysian trumpets to stir it up?
In my 10 gal shrimp tank, I have about 1.5" of pool filter sand, also known as silica sand. It was about $6 for 50 pounds at a pool supplies store. I like it well enough, grain sizes are bigger, but as for the cherries I regret not getting a darker substrate. A black sand would really bring out the colors in a significant way!