Textract Service Quota

There is no additional charge for quota increase, you will only be charged for the consumption. https://aws.amazon.com/premiumsupport/knowledge-center/manage-service-limits/

You can request for an increase in quota through service quotas - https://console.aws.amazon.com/servicequotas/home

The new limit value depends on your business needs i.e. how many documents do you want to process per second, how many records can your application handle/consume per second, etc. Also, you may need to look at the need to increase the limit for 'GetDocumentTextDetection throttle limit in transactions per second' if your application code needs a higher value for this API as well.