Look at the bottom left or right corner of the card for 2 numbers separated by a backslash
We don't expect to see Sunscour follow the same path, but it's notable how good 'free' spells, which require you to pitch a card to get their effect, have become in recent years
If your table plays long games, add lifegain or recursion so you can re-buy the shield and keep the cards flowing
Rather, I prefer to use a difficulty rating more akin to the Gears of War Series
However, an MP sale at $145 sets a high benchmark, with an NM copy setting an upper limit with a sale of almost $245
Key factors for timing: the current position is stable at ~14,000 after 12 months with the launch correction complete