You could do something like the following, if you will always have 2 product prices, with 1 that has a quantity of 1.

select ProductID, ProductName, CategoryID, CategoryName, pp1.ProductQuantity, pp1.ProductCost, ppo.ProductQuantity, ppo.ProductCost

from Product p

inner join Category c on p.CategoryID = c.CategoryID

inner join ProductPricing pp1 on p.ProductID = pp1.productID and pp1.ProductQuantity = 1

inner join ProductPricing ppo on p.ProductID = ppo.productID and ppo.ProductQuantity <> 1