Power Artifact Price Trend: 32,88 € From(Ex+): 45,00 €
Reducing costs is always great, but it is even better when cost reductions result in something degenerate. On Basalt Monolith and Urza's later variant Grim Monolith reducing the untap cost by 2 allows you to generate an arbitrarily large amount of colorless mana, which can win you the game with cards as new as Walking Ballista, but also with Alpha cards like Braingeyser or Fireball.
Infinite combos have been exciting players for decades, but this may be one of the first ones which were ever found. While there are two card combinations that don't need a third card to deal the winning blow after going infinite in more recent sets, in the golden days of early Magic things were not that easy. Therefore Basalt Monolith and Power Artifact have received renewed attention from players of the Old School format.
The entire last year (2016) the offer count here on MKM swung back and forth between 80 and 140 copies. Individual copies were selling somewhere around 20 € (15-25 € depending on condition). Starting in late December we saw a continuous decline in offered copies, accompanied by a quickly rising price, approaching an average of 30 €. With the natural interest of Old School and Commander players consistently outpacing the amount of copies getting listed, the offer totals kept going down on MKM and in other places. On May 7, there were 22 copies sold instead of the usual one or two per day, and another 11 copies left the market two days ago. That is not a lot of movement if you count in playsets, but given the low amount of listed copies this left the market devoid of “cheap” copies. We might see some copies relisted in the upcoming days, but the card will hold a new price of 50 €, especially given that the American price has even spiked considerably higher.
The card shouldn't be all that rare though. Considering the rarity distribution of the Antiquities set, there were three times as many copies printed than there were printed of Mishra's Workshop. I would guess that there are more players actively using decks with 4 Workshops than there are decks with 4 Power Artifact. With 121 Workshops available on MKM at the moment, there should be a lot more Power Artifacts available for sale in theory. The big difference is that Workshop has always been considered a desirable card, while Power Artifact has been forgotten for 20 years. This means that you should dig through your attic to find your copies and sell them in the upcoming months. It also means that there are lots of copies sitting in binders and old collections gathering dust somewhere, with their owners not knowing about the recent price movement. Maybe you can take advantage of that knowledge?