With AWS Step Functions, you pay only for what you use. Step Functions has two types of workflows: Standard Workflows and Express Workflows.
AWS Step Functions Standard Workflows pricing details
You are charged based on the number of state transitions required to execute your application.
Step Functions counts a state transition each time a step of your workflow is executed. You are charged for the total number of state transitions across all your state machines, including retries.
The Step Functions free tier includes 4,000 free state transitions per month. All charges are metered daily and billed monthly.
For details, see the Step Functions pricing examples.
AWS Step Functions Standard Workflow State transitions pricing
AWS Step Functions Express Workflows pricing details
With Step Functions Express Workflows, you pay only for what you use. You are charged based on the number of requests for your workflow and the duration, the time it takes for your workflow to execute.
Step Functions Express Workflows counts a request each time it starts executing a workflow, including tests from the console. You are charged for the total number of requests across all your workflows.
Duration is calculated from the time your workflow begins executing until it completes or otherwise terminates, rounded up to the nearest 100ms, and the amount of memory used in the execution of your workflow, billed in 64-MB chunks.
You may incur additional charges if the operation of your application workflow utilizes other AWS services or transfers data. For example, if your application workflow invokes an AWS Lambda function, you will be billed for each request and for the duration of each Lambda function. For details on AWS service pricing, see the pricing section of the relevant AWS service detail pages. Links to pricing for some of the commonly used services follow.
External data transfers to and from Amazon EC2
Requests and duration
On-Demand, Reserved, and Spot Instances
Fargate and EC2 Launch Types