Customize Estimate with default line item charge

Good question, KJ110.

You can create a recurring transaction for Estimate and enter a default line item charge. Here's the process of creating a recurring transaction:

1. Go to the Gear icon and choose Recurring transactions under Lists.
2. Click New. Then, choose which transaction as the Transaction Type. In your case, choose Estimate.
   
3. Fill in the necessary information.
4. Click Save template.
   
   

You may also want to review the recurring transactions you made in QBO: Review your recurring transactions in QuickBooks Online.

For additional reference, you might want to read through this guide on how to customize invoices, estimates, and sales receipts.

You know where to find me if you have additional questions about recurring transactions or anything QuickBooks. I'm more than willing to help. Have a great day!