I would be designing this in Java, and will create a GUI for it.
Will you provide the websites, and each state that each website is associated with? Or will the websites have an option of selecting a specific state and then we search a product that way. Also, by "websites that you choose" are you referring to giving the programmer a list of websites, and you can choose websites to search out of the list?
As far as filtering out duplicates, I would probably filter it out by name of product, but realistically it probably will NOT be 100% unique products that will be displayed after the search.