Display Product Cost based on Quantity

Plug-ins like product addon and product bundle calculate the cost, and provide a preview cost, at the product page level based on your selections before adding to the cart.

But if it is a simple or variable product and you change the quantity from 1 to 2 a calculation is not made on the product page.

Aim: Provide total cost preview on product page based on quantity selected.

Can you point me in the right direction? Thanks