The short answer is:
You are correct - the official HubSpot NetSuite integration does not support NetSuite Item Groups, and this exclusion is likely due to the Item Group object’s slightly different internal structure compared to Assembly and Kit Items, making it a low priority for the native connector developers.
The best solution is indeed a custom integration, but it doesn’t have to be prohibitively expensive.
By leveraging the HubSpot API and the NetSuite REST API in a lightweight, serverless environment, you can build a more precise, cheaper, and future-proof sync for Item Groups than relying on expensive third-party platforms or the official connector’s limitations 
The long answer is:
The challenge you face with Item Groups not syncing is common when relying on pre-built, one-size-fits-all connectors, as they prioritize the most-used objects.
While building a custom sync using the NetSuite REST API and HubSpot API initially requires development time, it is ultimately a superior and cheaper solution than relying on complex, subscription-based, third-party sync platforms.
The cost of a dedicated sync platform or the official integration’s lack of flexibility often outweighs the one-time development cost of a custom script, especially if you have other unique data synchronization needs down the line.
To execute this efficiently, you would use the NetSuite REST API to first extract your Item Group data.
A simple, custom script would then process this data, mapping the Item Group name and its constituent members precisely to your desired HubSpot Product properties or even a custom object in HubSpot.
Finally, the script would use the HubSpot API to create or update the corresponding Products in HubSpot.
This approach is better because it allows you to control the sync frequency, define custom mapping logic for specific fields, and ensure that only the necessary Item Group details are pushed to HubSpot, keeping your CRM clean.
Furthermore, integrating Google Tag Manager and a server-side environment like Stape or Google Cloud Platform makes the solution even more cost-effective.
You can host your custom API-to-API script on a cloud platform like Google Cloud Functions, leveraging their pay-as-you-go, serverless model.
This means you only pay for the exact compute time used during the sync, making it dramatically cheaper than monthly subscription fees for a third-party service, while still providing a robust, scalable, and highly customizable data pipeline that resolves the specific Item Group problem permanently.
This comment was generated with the assistance of an AI tool, incorporating my expertise in integrations 