This has been done I'm sure, but I don't think it's been done since Adventures.
So what is the most points your Fairgrounds can be worth?
1) Without Black Market in the kingdom.
2) With Black Market in the kingdom.
My answer for #1:
Kingdom is:
Young Witch, Tournament, Knights, Page, Peasant, Hermit, Urchin, Fairgrounds, a looter Marauder (Thanks AdamH), a Potion-cost card, and a Prosperity card
7 cards available in every game.
+10 kingdom cards.
+1 for Bane
+5 for Prizes
+9 for having all Knights
+4 for Page upgrades
+4 for Peasant upgrades
+1 for Madman
+1 for Mercenary
+5 for Ruins
+1 for Spoils
+1 for Potion
+2 for Platinum & Colony
+3 for Shelters
Total: 54 = 20 point Fairgrounds
For #2, I haven't done all the work, but:
The Kingdom could be the same except replacing a card with Black Market (plenty to choose from, just not Page, Peasant, Hermit, or Madman). So then it should just be a question of how many official cards exist, which plenty of people probably know off the top of their head.