Sand is not that hard to do. I would suggest getting PFS(pool filter sand) from your local pool supply place. I just bought three 50lb bags for $21. Lowes or HD will have play sand but it's very dirty and somewhat smaller than PFS.
PFS will not affect your water and is very clean straight out of the bag. I usually poor it right into the tank without cleaning it. Make sure your filter intake is positioned far enough away from the sand so that it won't go into your filter because of your fish stirring it up.
Depth really doesn't matter. I tend to fill it up until it gets to the plastic molding at the bottom of the tank. When you do water changes, just slightly stir it around to avoid dangerous build up of gases in the sand. You will see bubbles come up when stirring it around. I like to keep my sand shallow(1-1.5") so there are no chances for gas build up.
One 50lb bag will be more than enough, you will probably have some left over. $7 for substrate..... much better than paying Petsmart prices
