as per rjp14:

"save prices by date and display pricing data taken from multiple dates. Using something like a plot to see how a cards value has increased and decreased over time"

So basically MA should backup current price lists before each update and be able to parse them to produce:

simple graphs to reflect price changes

and/or

highlight changes in price for individual cards and display them in a separate grid column, using colors or other means (little arrows or other icons)