PC partpicker will tell you, on a daily basis, which sites have the lowest price on any given part at the time you check. Rarely, there might be a better price that hasn't been updated yet on PCPP, but not usually.
https://pcpartpicker.com/list/
As far as the Black Friday and Cyber Monday deals are concerned, you are really only going to see good deals on products from the previous year or two that either did not sell well or that they are trying to reduce stock on. For any current, "hot" products, your best bet is to simply watch for ongoing sales at ALL times. BF and CM aren't going to offer good deals beyond what you'd normally see on those products, and probably the prices will be WORSE when you get close to those days as inventory begins to run low. Supply and demand. When demand is high, as it is near the holidays, then newer gear goes up in price.