Back-to-school pricetag: $18.4BSurvey: Consumers are expected to spend an average of $563 on computers, shoes and other stuff, up 6.9% from 2006.By Parija B. Kavilanz, CNNMoney.com senior writerJuly 17 2007: 7:57 AM EDTNEW YORK (CNNMoney.com) -- Consumer electronics - such as computers, iPods and cellphones - are expected to charge up this year's back-to-school sales to an estimated $18.4 billion,