This sounds like it might be easier to with EMR.
You mentioned in comments you are doing computer vision. You can make your job hadoop friendly by preparing a file where each line a base64 encoding of the image file.
You can prepare a simple bootstrap script to make sure each node of the cluster has your software installed. Hadoop streaming will allow you to use your image processing code as is for the job (instead of rewriting in java).
When your job is over, the cluster instances will be shut down. You can also specify your output be streamed directly to an S3 bucket, its all baked in. EMR is also cheap, 100 m1.medium EC2 instances running for an hour will only cost you around 2 dollars according to the most recent pricing: http://aws.amazon.com/elasticmapreduce/pricing/