Finding Sum of Calculated column

Hi All,

I believe this problem might have an easy solution but I'm not too sure.

I'm wanitng to find the total cost for a product with mutiple ingredients over a selection of past months when prices differ.

I've taken a simplified version of the two tables im using (below) which are connected via Ingredient ID with a many-to-many relationship. (ignore etc.)
BOM: 

Component Cost:

I'm trying to get a total cost for each product, which can vary depending on the month (ive not included date table here).
For product 1 in July, I've created this table and would like the Total Product Cost to add up to equal 1.5+425+6+154 = 586.5  but at the moment its giving the multiplied sum of Quantity and Price tables. 

The formual I've used for Total Production Cost measure is below, I know it's wrong as I'm using sum on the columns but have no idea what else to use.