[A] If you are facing the problem of BOM cost showing "0" price as shown below if you are checking default pricing, then go to Inventory module.
[B] Search the product in the inventory module and check the price saved in master, as you can see below item ABC123 is showing price "0" in inventory master hence it is showing "0" in BOM cost.
[C] As you have chosen Default Pricing for BOM cost, the costing is based upon the prices saved in inventory master.
Keywords - Wrong BOM cost, zero BOM cost