For your scenario where data has to be copied from one source to another, you can simply create a pipeline and use a Copy activity.
- Copy Activity runs on Azure IR. It won't need any cluster
- Cost depends on execution time of Copy activity and number of DIU units configured in activity. Search "ADF Pricing" for more details.
- Spark clusters are required when you use the data flow inside ADF
Please don't forget to Accept Answer and Up-vote if the response helped -- Vaibhav