Amazon has a handy page that details everything under their free tier here: http://aws.amazon.com/free/ A single Micro instance running for 744 hours is free of charge, means you will be able to spin up two micros for half that alotted time, or three for a third. As soon as you go above 744 hours of micro compute you will be charged the standard $0.02/hr pricing. If you're really cost adverse you can set up another Amazon account, the free tier last for 12 months and the Credit Card you need to provide is allowed to be the same for the accounts.