More money for more volume

I know that if you are a regular customer that brings in a lot of scrap some scrapyards will pay you more than someone who brings in scrap once a month. So my question is, What does it take to get a higher rate? More or less talking non ferrous metals, how many lbs of aluminum would it take to get a better price? 1500? What about copper,brass, etc etc. Have you ever gotten a better rate with just one large load as opposed to loads every week.