Tough to track exactly because you have to know where you are buying it from and how much. Retail small quanities are more than truck load wholesale quanities. Bag is more than bulk.
For instance in 2004 I was quoted $100 ton for buckwheat at the breaker for a 24 ton load. Last year it was $160 ton. This year it will probably be $180 a ton due to diesel prices.
Look at the threads on what people pay that year.2011-2012 Anthracite PricesCoal Prices 2010-2011?