Change the formulas in columns M and N so that they only contain the INDEX part of the formula to give a unit price, e.g. =INDEX(PriceList[Price1],MATCH([@Item],PriceList[Item],0)) and change the column header to Unit Price1 (repeat for each price column in the price list),then add the multiplier, *[@[SUM Qty1]] in another column, e.g. [@[Unit Price1]]*[@[SUM Qty1]]
Then you could use a simple SUMIF formula in column R, e.g. =SUMIF(Main_090719[Unit Price1],[@[Price]],Main_090719[SUM Qty1])
As you have multiple columns, you will need a sumif formula for each of them, then add the results together.