Amazon Prime members spend an average of $1,224 a year

"Prime members are great customers for Amazon. In 2012, they were about 4 percent of Amazon's 182 million active customer base. But they accounted for nearly 10 percent of purchases, because they spend more than twice as much as non-prime customers—$1,224 a year versus $505."
Source:  Business Insider, 11th March 2013