10: Curse, Copper, Estate, Silver, Duchy, Gold, Province.
= 10
+3: A couple of Alchemy cards costing a Potion, bringing with them Potion.
= 13
+4: A couple of Prosperity cards, bringing with them Platinum and Colony.
= 17
+6: Tournament, Followers, Trusty Steed, Princess, Bag of Gold, Diadem.
= 23
+1: Fairgrounds itself.
= 24
+2: Hermit, bringing with it Madman.
= 26
+7: Marauder, bringing with it Spoils, Abandoned Mine, Ruined Laboratory, Ruined Market, Ruined Village, Survivors.
= 33
+10: All ten Knights.
= 43
+3: The tenth Kingdom card is Young Witch, bringing with it a Bane (which happens to be Urchin, bringing with it Mercenary).
= 46
+3: Hovel, Necropolis, and Overgrown Estate.
= 49
There you have it. With the set described here, it is possible (with extreme luck, and the negligence of your opponents) to make your Fairgrounds worth nine points. Fairgrounds reaches just short, by one tantalizing cardsbreadth, of having the potential to be worth 10 points, as much as a Colony.