Install stock_product_price_update_mac5 module and go to Inventory > Configuration > Products > Update Product Price

The list view is editable so you can edit the cost price and sale price of each product easily. You can also use default filters if needed

You can also export this to excel. From the Update Product Price list view, select products you want to export and click Action > Export

From the Export Data window, you can select the Update Product Price Export on the saved exports for easy filling of fields needed. Then click EXPORT TO FILE button