Personally, I pay per piece. What I'll do is look at a bunch of an item (RAM, Finger Cards,...) and then will figure out what I basically want to pay per pound. Then I divide that out by how many are in a pound, and round down to the nearest "neat number", and you have a price per item. It's much easier for me to count than to scale. On some pieces, you'll lose a little, but if you do the math correctly, you'll be where you want to be on 90-95% of the pieces.