I disagree. If you have an polymorphic getPrice() as part of an interface than you can't possibly list all the invariants as individual well-typed exceptions.

I disagree. If you have an polymorphic getPrice() as part of an interface than you can't possibly list all the invariants as individual well-typed exceptions. That would assume perfect knowledge of all possible implementations of that method now and in the future. That's not OOP. In a non-polymorphic case of a bundled item, you'd simply not have a getPrice() method on the item at all. It might simply not implement the PricedItem interface, for example. There are plenty of ways of ensuring all invariants are met, in a type-safe way, without using exceptions. If it's possible to come to situation as normal correct operation (such as an item in bundle) then it's not exceptional.