I'm actually a bit more correct than that

With a proxy server, you have a traffic flow along the following lines:

client -> IN proxy -> OUT to Internet -> IN to proxy -> OUT to client

So all of your bandwidth at the proxy is used twice if you're accessing it over the Internet, as you are in this case.

So you're correct that Amazon only charges for outbound traffic but 1Mbps of traffic being downloaded by the client will result in 2Mbps of OUT bandwidth at the proxy, and will appear on your Amazon usage.

I've conducted some fairly accurate tests of bandwidth utilization when using various Internet streaming services and the figures I quoted above are accurate.

Also, you lose your free tier access a year after you first set it up, regardless of usage - so unless you create a whole new account you only get the first 1Gb free.