There are a couple of options you could use for bulk editing.
1. Under the Products tab, Quick and Bulk Edit please enable the options under this section. Then navigate to Products > All products, select the relevant products whose cost you want to edit and select Bulk Edit
2. In your WordPress dashboard, navigate to Tools > Bulk Edit Costs here you will find all your products, along with variations and you can edit their costs.
3. You can import the costs. First under the Advanced tab in the plugin’s settings, enable the compatibility with the WP All Import plugin. Then download and Install the plugin and Import the costs using the plugin.