Calculation Basis Value
The rebate calculation references the item record for the calculation basis value. These values are either user-defined costs or calculated by the system. The unit cost of an item is multiplied by item quantity to populate the Est. Extended Cost value. See Cost Estimate Types in NetSuite OneWorld.
Unit costs are on the item records, not on the agreement details. But if you select Rebate Cost as the calculation basis, the system uses the value from the agreement details. If there's no corresponding value on the item record for the selected calculation basis on the agreement details, the corresponding calculation basis amount of the item is considered as zero.
Some for receiving rebates use the estimated extended cost value and divide it by the item quantity to get the unit cost or the calculation basis value.