QB Issue Resolution:

create the item, zero rate, and use it

that is the best it gets for a line item comment, the price of zero will show, nothing can be done about that.

Or if the policy could apply to all, put it as a comment in customize forms footer area

Resolution for Issue 'We want to add a comment about our shipping policy to end of selected estimates. How do we add a line item in items that is just a “note”?' available: Yes (Solved).
Source: Intuit Community forum.

We want to add a comment about our shipping policy to end of selected estimates. How do we add a line item in items that is just a “note”?: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

Support for comment
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Error Recovery for comment [Canada]
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