my buddy D used to buy DXM by the bottle. Usually 25 or 50 gram bottles. He capped them up w/ .5 grams in each one (give or take a small amount, he weighed it out w/ a digi scale, then realized how full the cap would have to be. then he just eyeballed.) he usually charged 5-6 bucks a cap, and in bulk purchases 3-4.
.5 grams of dxm is like 6 oz of robotussim, you figure 333 for 4 oz, 666 for 8 oz (or is my memory fucking with me again?).