AWS EC2 offers a dynamically priced product called Spot Instances (http://aws.amazon.com/ec2/spot-instances/)
Our system is designed to let you control when servers are turned on or off in order to perform orderly computing. Likewise the fact that the servers and drives are persistent allows you to shut them down and back up again over peak times and keep data persistent. This is great if you are doing large jobs like 3d rendering for example.
Best wishes,
Patrick Baillie CEO