It cost 5 million TODAY, after the man has been dead for ages and the price went up.
Okay, there are a many artists whose current works sell for hundreds of thousands of dollars, or more. The point is, price is determined by supply and demand. If there's enough demand (people sleeping on the street waiting to buy it when it becomes available) they can charge more. If not (»en.wikipedia.org/wiki/HP_TouchPad) they can't.