What is the most expensive beer that can be purchased in the United STates?
How are you defining “purchased”? At a bar or liquor store, or over the Internet?
Pharaoh’s Gold bills itself as “the world’s most expensive beer”.
http://www.pharaohsgold.com/
I can’t tell if it’s a joke or not.
And there’s this.
http://www.poynter.org/pointssouth/2002/editions/ps1/sloan.htm
The last time I was in the Brickskeller pub in Washington, D.C., they had priced a 3-litre bottle of Duvel at about $70.
Sam Adams produced their Millenium Triple Bock, and that went for, IIRC, $300 for a 1L bottle.
From: http://www.samadams.com/beer/styles/millennium.html
The bottles contain 750 ml.
In 1987, while drinking at the Brickskeller in D.C., I purchased a 12 oz. bottle of Samichlaus for $5.50. I still have the bottle. 
What ever the opposite of Crazy Horse is.
I always understood the most expensive beer was sold at football games.
That last beer-for-the-road before my DUI.
I can confirm that. I has perhaps the equivalent of $100 of Sam Adams Millennium at the 2000 Great American Beer Festival in Denver. If God were a beer, He would taste like Millennium … it was extraordinary, and unlike SA Triple Bock, very drinkable.
That just sounds wrong on so many levels.