You may have some products in your Shopify store that are subject to taxes such as GST (Goods and Services Tax).  The line_items.price field in the Shopify Order API will include this.

You can use the formiula below in the Calculated Fields to export the line item unit price before taxes from a Shopify order:

{{ line_items.price }} - ({{ line_items.tax_lines.total_price }} / {{ line_items.quantity }})

The formula simply subtracts the total tax applied to the line item divided by the ordered quantity from the price.