Hello LukeDuke007
Thanks for your post.
The field "_alg_wc_cog_cost" has nothing to do with ATUM.
ATUM stores all the information in custom tables.
Please, take a look at our ATUM Export PRO Premium add–on.
One of its features allows you to export and import any data in your WooCommerce on CSV files.
So, you can generate CSV files to import the info about your purchase price without any problem.
All information about how works the Premium add-on you can find here.
Best regards,
Iryna