Unfortunately there isn't a current easy way by Shopify to provide discounts for products added. In the future Shopify may offer an easier way to do this, and we would revisit it. Other apps get around this by duplicating products.
In the meantime, a solution which may work for some, would be to create a duplicate of the product you wish to offer at a lower rate as an accessory, reduce the price, and then hide it from the rest of your shop by following this tutorial HERE.
Then, if that product is added as an accessory, it will then only be visible from within the Product Accessories app.
Please keep in mind, that the reduced price product, and the original product's inventories will not be able to be linked.