If you have a lot of apples to process, it's well worth the purchase. Mine's from the Pampered Chef. It clamps onto the counter edge (I have to use it under the dishwasher mount, since the lip of the counter is too short elsewhere). There's also a kind you can get that uses suction on the countertop. I don't know how it compares for stability.
They run less than $20 and are available from Amazon and most general cookware places.