Thanks for posting this question. While I'm checking on this, just to clarify, are you referring to this doc Azure OpenAI on your data (preview)?
Chat with Azure OpenAI models using your own data
Just adding relevant FAQ:
https://learn.microsoft.com/azure/ai-services/openai/faq#how-much-does-it-cost-to-use-azure-openai-on-your-data-
How much does it cost to use Azure OpenAI on your data? When using Azure OpenAI on your data, you incur costs when you use Azure Cognitive Search, Azure Blob Storage, Azure Web App Service, semantic search and OpenAI models. There's no additional cost for using the "your data" feature in the Azure AI Studio.
Kindly let us know, I'll follow-up shortly.