Option 1: Being in standard or average costing method will allow you to Compute from BOM. If you are using FIFO, before opening inventory, you can switch the product to standard and take advantage of this feature.

Step 1: Go to the App of apps, remove the default “Apps” filter, search for “bom”

Step 2: Install this module name “Product Extension”

Step 3: Now on your Products with a BOM set AND in a category set to Standard or Average Cost, you will see this button “Comput Price from BoM”, if you give it a click it will update the Cost on the product to the sum of component costs.

Option 2: Go to your Bill of Materials and you can view the Structure & Cost as a report that can be printed, you have a few options (see image) 

Option 3: Go to the Bill of Material menu item, select 1 or more BOM’s and use the Print action to download a PDF
 

Option 4: If you prefer to have an excel format, build an Export in the Bill of Materials using “Export all Data” and then Go into the BoM lines, into the Product Template, then locate the Cost field. You can download to Excel and use a function to sum the costs in Excel.