Hi,
Please let me know as mentioned in the below link. Do we have to click “Update BOM Cost” button for every method?
https://kb.erpnext.com/kb/manufacturing/valuation-based-on-field-in-bom
In ERPNext, pricing is usually fixed unless you want to change it.
If you are doing project costing, you should create a new / duplicate BOM to maintain historic prices.