In QuickBooks Online, you can create a sub-customer for a job estimate. Then, include the item in the transaction.
Step 1: Create a sub-customer.
Go to the Sales menu.
Within the Customers tab, scroll to the customer you are preparing the Estimate for. (If your customer was not yet set up, click on New Customer at the top right of the Invoice screen to set up your customer.
Tick the Is sub-customer box. Then, select the name of the customer you want to associate it.
Click Save.
Step 2: Create Estimate.
Go to the +New button.
Select Estimate.
Complete Estimate form with the date, product/service, description, quantity, rate, etc.