[JWait]

I don't understand why you would want to do this? If the product is $50 regardless of how many a customer buys there is no reason to change anything. If you had the option of a customer buying 10 and getting a discount, then that is something else entirely. and you can do that through the product options section.

You also have the option of having the customer adding something to their cart and remaining on the same page they are on, or being sent to the cart when they add a product where it shows the total for the items they added.