On Import from Buylist
The cost of an item is set on the buylist and can be edited while importing the buylist item into a batch. For instructions on importing a buylist item into a batch, see the Buylist section of Adding Items to Batches in PREP & SHIP
In a Batch
The cost of an item may be edited after the item has been added to a batch -- see Editing a Batch Item
Changes made in the batch and saved will update the buylist item.
After Listing / Shipping
The cost of an item may be edited after the item has been listed / shipped in the same way one edits an active batch item before listing or shipping. If you edit the cost of an item in a batch, even after the item has been listed and shipped, the cost will be updated / changed on the buylist item associated with the item.
For instructions on how to edit a batch item, see Editing a Batch Item