Standard Costing V Actual Costing in Retail

I would like to create standard costing for one vendor. I am using AX version 4! When I set up SKU method FIFO standard costing do I need to set up price. I need to go to Price & Discount & imput price. Then I go to purchase order when the invoice arrives & post the invoice using actual cost.

What is the best method? I receive the invoice sometime after the item is sold. We need to record the cost at the time of sale. Currently we are using weghted average but some stock is sold with 0 margin.

To recognise the cost my manager advised we need to use standard cost upload to the system. The question is how I uploaded standard costing? How I upload the actual cost? The system will alocate variance to P&L.