BlinkBid gives you options when displaying a line item with a rate of "0".
Go to Settings < Document Appearance < Label & Section Text, Line Items and Categories.
Choose "Blank" and no rate will appear for the line item.
Choose "Zero" and a value of "0" will appear as the line item rate. You can use this to show a client they are receiving a particular service but not being charged for it.
Choose "Custom" if you want to enter text. For example, line items with zero values can appear as "TBD".