Like Equipment before it, it was a reminder that all the hours of playtesting and scads of design philosophizing cant quite compete with an army of millions of Magic players determined to break new card types
The stock has slowly been dwindling as more fans realized how good this card is, and it seems like the market supply suddenly started to run out
On the other hand, for products like Secret Lair drops, Commander decks, or other preconstructed / box-set supplemental products, we used the cost of buying the sealed product (which is generally lower than the cost of buying all of the cards in the product individually) from around the time the set was released (for sealed product, you'll often pay much more if you wait until the set goes out of print to try to buy it)
It is still hands down the most cards you can get for the mana overall but it comes with so many penalties that it is hard to use well
Average doesnt tell us the whole story, however
If we can build a board and get in a hit with Lightning, its first strike damage will happen first, which will then double the damage from all of our other creatures when they connect for normal damage