Your account will be charged for setting a task and the number of results you will get in the items array. The cost can be calculated on the Pricing page.
Setting Apple App Searches Tasks
This endpoint will provide you with a list of apps ranking on the App Store for the specified keyword. The returned results are specific to the indicated keyword, as well as the location and language parameters.
Your account will be charged for every 100 results returned, e.g., if you specify "depth": 101, you will be charged as per 200 results.