It's an artifact, there is a reason there isn't a listed price.
Now, as to how much it could be worth? Look at what it could theoretically do (anybody in the market for a Deck of Many Things would probably research it quite well).
The Fates, and Vizier provide artifact-level save-your-rear type effects, the sort of thing normally reserved for very well worded wishes, divine intervention and Epic spells. Their theoretical value is almost any amount of money.
Comet, Gem, Jester, Key, Knight, Moon, Star and Sun all provide strong, but mortal-range benefits (wishes, inherent ability score increases, treasure & magic items). A few give free XP, but that can be earned over time.
Then there are the bad cards, real bad trouble. The sorts of things you'd wish on your worst enemy.
So, since most of the good results are about equivalent to about 2 wishes (1d4 wishes, +2 inherent ability boost, loads of treasure/jewelry/jems), an average "good" draw has a value of around 50,000 GP. Those two really good cards have a value that is approaching priceless.
I'd assume it could probably get a value of a 100,000 GP or more from somebody (possibly up to 250,000 from somebody who was rich and feeling lucky, hoping to get at least two good draws in a row), and not just an idle wealthy noble. These things can be very dangerous, and anybody who would be bidding on one would probably know that. Other adventurers, high priests, archmages, crown knights, these are the people who would be in the bidding (as they're also the kind of people to have this kind of money).