Notification system to track the ups and downs of cards/products

Possible feature related to prices: I really like being able to see the "daily winners" and "daily losers." I don't know how you are pulling that information on the back end, but I've been thinking about the possibility of being able to target specific cards to see their recent price changes. This would be like a "watch list" where I could choose, say, 10 cards from my collection to have on their own list to see percent price changes in the last couple days. The reason I'm asking about this is that premodern is becoming more popular and a lot of older cards I have are suddenly spiking in price at various times. So I was wondering about being able to flag certain cards to track them more closely. Even better would be to be able to choose cards for a watch list, and then get notifications (email, etc.) in the future when they experience bigger price fluctuations.