Vera does wonderful research (and writes it up, just like you have to in school!) in her weblog. Most recently she enlightens us about butter, guns, and a precursor to the slide rule. You can actually keep track of butter prices online. Which reminds me, the NY Times had an article on the difference between French and American butter. French butter has more butterfat and the premium ones are made with a time consuming process that includes a ripening period and churning in small batches. It makes a big difference for those yummy French pastries. There are some American butters that feature higher percentages of butterfat, and you may also be able to find imported butter at an upscale market.