I apologize for any confusion, @PAlcala. Allow me to clarify things by sharing some information.

QuickBooks Desktop typically uses the average cost method to calculate the cost of goods sold (COGS) for assembly items. This means that it takes the average cost of the component parts used in the assembly to determine the cost of the assembly item. The cost you see on the assembly item screen is usually the most recent purchase cost and is not necessarily the average cost.
 

If you want to ensure that the BOM cost is used for calculating COGS, you may need to explore third-party tools or extensions that integrate with QuickBooks Desktop and provide more advanced features for managing bills of materials and inventory. These tools can offer more flexibility and customization options for tracking and updating costs based on your specific needs. You can find one in this link: Apps help QuickBooks run better. 
 

It's also important to consult with your accountant or financial advisor to ensure that you are using the appropriate costing method and accurately tracking your inventory costs in QuickBooks Desktop. They can provide guidance based on your specific business requirements and industry practices.

Furthermore, once your client has approved your estimate and agreed to a predetermined sum instead of paying based on actual time and expenses, you have the option to convert the entire estimate into an invoice. If you'd like to gain further insight on this topic, please feel free to check out this article: Create an invoice for an estimate in QuickBooks Desktop.

I'll be around here in the Community if you have further assistance managing your inventory in QuickBooks Desktop. Just hit on the Reply button