About the only way you'll find this is to get in contact with someone who builds systems and get them to allow you to look at the price lists that they've downloaded from their suppliers over this period of time.
But I don't think that you'll have much joy here as if most people are like me they dispose of the ones over 6 months old as unless they have something outstanding like an insurance quote most don't allow this data to waste space on their HDD's.
You could always look through Computer Mags on line as the adverts in these quite often have prices and if you can access the archives that will give you some data to work with. But you'll have to remember to take into account fluctuations in the $ as well as this can affect pricing. Unless you can directly access the manufactures sites and gain access to their price lists in the native currency I think that you are going to find it difficult to get the required data.
Col