What a difference 5 years make!
Back in 2004, in response to OP's request for suggestions re. champagne around $10 a poster said
"Not to be too pedantic, but what you will be getting around $10 is not Champagne but sparkling wine. "
Fast forward Nov 2009:
"We are going to offer champagne for fewer than 10 euros (15 dollars) a bottle for the holiday season," said Christophe Blaise, Carrefour manager in Reims, the Champagne region's capital.