I am giving you a link of website from where you can get all of the historical prices of resins since 1997. You have to open the website and in the top, there will be a column where you will put the starting date and the ending date. Then press prices and you will get all prices of the resins between that period. I hope this site will help you!
Resin historical prices from 1997 to 2008
Resin historical prices from 1997 to 2008