IDK if this would be a good idea, but this is what I would do. I would give him a really low continual price (Low ball him), then y'all negotiate until you can find a low price that suits him and you, and can cover costs if the price goes low. That way, if prices go up, you make more profit. If prices go below what you are paying him, you have a buffer of money from when the price was up to cover your costs until prices go up again. Just my $.02.