With Pro, any card page has a Watch the price button. Pick a grade the card has a sale at, and the Monday email tells you when the latest sale at that grade moves a tenth either way, or 5% or a quarter if you choose. A card is reported once per move, then watched from the new price.
Or name your own price. Set a target on any watched card, one number: under the latest sale and the email waits for a drop to it, over it and the email waits for a rise. You are emailed once, the same day the daily price check sees a sale get there, not the following Monday.
Prices are rechecked in turn, a few cards a day, the longest unchecked first, so watching a card never slows the site down for anybody else. Your watchlist, with every starting price and every change, has its own page, where you can put it in order by the biggest move and download it as a spreadsheet. Cards you watch carry a star in Browse, and each card's page draws where its price has been since you started watching. Own one already? Note what you paid, and every row says how the latest sale compares, with the whole list added up at the top and an order that puts your best buy first. Each card also takes a short note of your own, like which binder it is in.