Which you can also do at Digital Ocean (note: you have to take a snapshot, and destroy the droplet in order to suspend billing).
While it might be pennies (or less!) - I'm still wary of how Amazon bills everything separately - your data at rest, your CPU, your bandwidth. I don't know if Digital Ocean would be any cheaper - but it sure strikes me as being a lot easier to predict. Maybe I'm just unreasonably afraid of what I perceive as "billing complexity" at Amazon.
Now I'm actually tempted to set up a small classroom using skolelinux/DebianEdu[1] on Digital Ocean built around a central droplet running the servers - and seeing how easy it is to suspend every thing to a dormant state and revive it... mostly just to play with the ldap-stuff.
IF you run it continuously. hyperdeficit was talking about using VMs for teaching, where VMs would presumably be spun up and down as needed.