Now you can enter the same supplier for all the variations. For this go to the ATUM Inventory tab within the product, and select the supplier.
Regarding the purchase price, you have to put in individually for each variation. However, if you want to make this process more quickly, you can use our premium add-on ATUM Export Pro. With this add-on you will be able to export almost any kind of data in your site, in this case, products, import it on a spreadsheet to modify it in a quick way, and then import it again to your site. This way it will be easier to set the same purchase price for all variations.
I leave you here the documentation of the add-on where you will find useful info about how it works: https://forum.stockmanagementlabs.com/t/atum-export-pro-documentation
And the link to the demo site in case you want to try the free trial: https://stockmanagementlabs.com/addons/atum-export-pro/