Calculated column with variable periods

create a new column in supplies

supply end Date = minx(filter(supplies,supplies[product id]=earlier(supplies[product id]) && supplies[Supply Date]> earlier(supplies[Supply Date])),supplies[Supply Date])

create a new column in sales

cost = minx(filter(sales,sales[sales_date]>=supplies[Supply Date]
&& (isbalnk(supplies[supply end Date]) || sales[sales_date] <supplies[supply end Date])),supplies[cost for 1 pc])

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Hi D3K ,

We can also create a  calculated column in Sales Table to meet you requeriement:

Cost Price for 1 pc =
VAR i = [Product ID]
VAR d = [Sales Date]
RETURN
    CALCULATE (
        SUM ( 'Supplies'[Cost price for 1 pc] ),
        FILTER (
            'Supplies',
            'Supplies'[Product ID] = i
                && 'Supplies'[Supply Date]
                    = CALCULATE (
                        MAX ( 'Supplies'[Supply Date] ),
                        FILTER (
                            'Supplies',
                            'Supplies'[Product ID] = i
                                && 'Supplies'[Supply Date] <= d
                        )
                    )
        )
    )

Best regards,