Prices....

When im on a website and i look at the bags, they usually tell me a price that they're selling the bag for but sometimes they dont tell you the original retail price of the bag. Just say for example i find a Christian Dior bag online, i go into the CD store to look for the original price (to see how much im really saving and if its worth buying from their website) but because the bag is either last/old season they dont have it in store anymore. So i check on the CD website and they dont have any details of the last season bag either. Where can i go or what can i do to find out the RRP these stores were selling it for? Sometimes i just type in the item name online and see what comes up.. and nothing. I just want to be able to compare prices... :wondering