For a 12-long, for a shallow look but with enough volume to prevent bare spots, you'll need between 6 - 10 lbs.
Dry is fine for a setup if you're planning on cycling the tank, one rinse should remove most of the dust from it. If you're looking to short-cut cycling time, live sand is going to speed things up.
Personally I have used both the dry and the live, and the only difference was a few days' worth of cycling.