I would like to use Amazon EC2 as an emergency backup database+web server in the event our primary host becomes unavailable. I feel like I wouldn't have trouble setting up a Windows instance, install SQL Server and get the web server up and running (would take a few hours, plus installing various libraries, our source code, etc).

My question relates to pricing. If I simply "stop" the instance rather than "terminate" it, does that stop counting "instance-hours"? I would prefer not to terminate the instance and lose all that work I spent setting it up. If I must "terminate" in order to stop the billing - is it possible to make an image of the server after I have set it all up, then save that image somewhere (S3?) Is this something that people do regularly?

Ideally this instance would just be waiting in the wings for an issue with our host, but costing us nothing except perhaps data storage costs.