I caution against using EP4 as a backup tool... There are suggested programs such as DrBytes database backup and simply exporting the database from phpmyadmin that will more thoruoghly capture all the necessary data to restore the site's data to the point at which it was retrieved.
That said, if this plugin is going to be used to backup data, a couple of things, and it is really this part that is covered in the instructions and a basis for operation: export, modify value, save as new file but with end of filename slightly changed, import the file, witness that change made to site matches intended action and witness that no other similar undesirable changes were made...
As to this cost field. EP4 does export cost export through a few different export paths, but if something were done to the database to add a field, then need to identify which field in which table is desired to be "preserved". If it is in the products table, then use the custom fields area in the EP4 configuration screen. If a field were added to a table outside of the products table and the field name is not already recognized and handled, then additional coding would be needed to add that field in where desired.
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