http://www.chron.com/disp/story.mpl/sports/other/5488159.html

Per this article, the Vikings average ticket price was the 12th highest in the NFL, and about $4 per ticket above the NFL average.
Still, the Vikings average price of $71.81 pales in comparison to the Patriots (highest at $90.91) and the Redskins (second highest at $88.59).
These figures do not include the cost of club seats or luxury suites, by the way.

Frankly, I have a hard time believing the average cost of a ticket to a Bengals game is only $66.05 when the cheapest ticket in the house is $64, and there aren't that many of those seats.
I'd guess the average cost is closer to $76.
Look for yourself....

http://www.bengals.com/tickets/StadiumMap.asp

EDIT: I'm guessing the Bengals average ticket price of $66.05 might be based on the majority of the tickets being sold as season tickets which are discounted somewhat (as are the Vikings).
Of course, you do have to pay a one time PSL called a COA (Charter Ownership Agreement) for each season seat you buy at Paul Brown Stadium