Microsoft Graph connectors index quota

Question

I'm having issue while understanding the index quota for Microsoft Graph connectors.

We're planning to develop an application that pushes data from a web application to Microsoft Graph using a external connector. Then it should be able to search these data from SharePoint. Initially we'll be having around 1000 indexes and can be no more than 10,000

From the license page, I saw that users need to purchase index quota for item indexing.

For that,

1. Do we needs to purchase Microsoft 365 E5 licenses for the organization to add up to 10,000 index quota ?
2. I checked Extra Graph Connector Capacity and seems it is not suitable for this use case since 1 million indexes will not be used at all and 1000USD per month is quite expensive. Is there any other plans with lesser number of indexes for cheaper price ?
3. Is there any pay-as-you-go pricing model for Microsoft Graph?
4. Finally, Is there any other alternative approach that can be used to achieve my end goal of showing our custom data in SharePoint search?

Appreciate if anybody can help.