With Elastic MapReduce you only pay for what you use.
Your cost will depend on the number and type of Amazon EC2 Instances in your job flow and the amount of time it is running. Elastic MapReduce pricing is in addition to pricing for EC2 and S3.
Pricing for Amazon EC2 and Amazon Elastic MapReduce
You are charged from the time the job flow begins processing until it is terminated. Partial hours are rounded up.
Save Money with Reserved and Spot Instances
The Amazon EC2 prices above are for On-demand Instances. On-Demand Instances are the most expensive but give you the most flexibility. EC2 also offers Reserved Instances and Spot Instances.
Reserved Instances give you the option to make a low, one-time payment for each instance you want to reserve and in turn receive a significant discount on the hourly charge for that instance. There are three Reserved Instance types (Light, Medium, and Heavy Utilization Reserved Instances) that enable you to balance the amount you pay upfront with your effective hourly price.
Spot Instances enable you to bid for unused Amazon EC2 capacity. Instances are charged the Spot Price, which is set by Amazon EC2 and fluctuates periodically depending on the supply of and demand for Spot Instance capacity. To use Spot Instances, you specify the maximum price you are willing to pay per instance hour. If your maximum price bid exceeds the current Spot Price, your request is fulfilled and your instances will run until either you choose to terminate them or the Spot Price increases above your maximum price (whichever is sooner).
"Amazon Elastic MapReduce with Spot Instances has made it easy to prototype and surprisingly cost-effective to scale, decreasing our data processing costs by over 50%." - VP of Engineering at Fliptop
To view more information and current prices for Reserved Instances and Spot Instances, see the Amazon EC2 pricing page.
Other Pricing Details
Amazon S3 is billed separately. (Many customers store their input and output data in S3; others store all of the data locally on HDFS.) Currently it costs $668 per month to store 10 TB of data in S3 with reduced redundancy. The more data you store, the lower the monthly price per GB.
Amazon SimpleDB is also billed separately. (Only applies if you enable debugging for your job flow)
If you choose the MapR M5 Hadoop distribution there is an additional charge. See the MapR detail page for more information and current prices.