This is one of the things which annoys me about AWS, and certain other providers which do a per GB cost on outgoing bandwidth.
We get around 50TB of data transfer per month from Linode, from having around $500/month worth of servers. The cost of using this much data with EC2 - around $5400 a month. It's not even close to being competitive.
you wouldn't want to do this straight out of EC2, but once you add S3=>CloudFront to the mix it's much less bad. Only thing you want to be serving from your EC2 boxes and load balancer is gzipped HTML/CSS/JS (could even do CSS/JS on S3/CF if you wanted).