According to this post on Luxist, the world’s most expensive beer (officially) is Vielle Bon Secours, which costs approximately $78 per pint at the Bierdrome in London. (Luxist incorrectly says $39 per pint; they got their conversion wrong—it’s about 39 pounds, not dollars.)
This beats out Sam Adams Utopias, which at $100 per 24oz bottle, settles in at just over $66 per pint. (I’m assuming 16oz pints.)
This is just the retail price; I’m not even going to go into auctioned vintage beers, like on ebay—that’s a whole different kettle of fish!
(A quick search on the beer indicates that it’s brewed by Brasserie Caulier, in Belgium, and I’m guessing it’s one of their Belgian strong ales.)