Somehow you need to join both tables; as we do not know the structure of these tables and how they are really related, it is hard to provide a precise answer.
This could be something like:
SELECT
a.Product
,a.Price1 + a.Price2 + b.Price3 as 'Total cost'
FROM
tbl_Products a
INNER JOIN tbl_othercosts b ON b.ForeignKey = a.PrimaryKey