How to update Estimated Cost against an existing Sales Order line
Whenever a line item is added to a Sales Order, the software copies the item's current Estimated Cost into the line. After that, the Estimated Cost against the Sales Order line is not updated by any automatic process. In other words, changing the item's Estimated Cost will not affect the Estimated Cost stored against existing Sales Order lines.
To update the Sales Order line item with the item's current Estimated Cost, you must delete and re-add the line item to the Sales Order. Prior to this, of course, you should make sure that the Estimated Cost looks correct for the item in question. Remember, the Estimated Cost for manufactured items is calculated by running the Batch Rollup in the Cost Rollup module. The Estimated Cost for purchased items (less likely to be present on a Sales Order) is determined by the Estimated Purchase Costs screen.