Amazon EC2 multiple instance management

We have a Client/Server setup where we have 1 Server and dozens, possibly hundreds of Clients that fetch jobs from the Server and do their work. The software for the Server and Client is already developed. We are looking for someone who can help us manage many Client instances in an automated fashion on Amazon EC2. We want to specify N instances and each instance is created and deployed and does exactly the same thing: runs an executable jar file. This is a custom search engine application. The jar files are programmed to fetch and process a specific list of URLs provided by the Server. When the URLs are fetched and processed, reports are sent back to the Server and the instance shuts down. We would pay Amazon for each instance usage by the hour, as opposed to the month. There is no coding involved. 100% sys admin work. We just need help interfacing with Amazon EC2 and testing the deployment of large numbers of instances (Clients). Experience with managing large numbers of Amazon instances and how they bill for services is essential. I look forward to your response and working with you on this.