I've had my current corker since Oct 2008. It's only done about 450 bottles, so far. Cost around $100. So 22 cents per cork inserted so far, or $6.60 per batch of 30. Price dropping constantly. Hopefully another 60 this sumer, bringing price down to about 20 cents per cork inserted.
I view the corker as equipment (like a carboy, and an Auto-Siphon), so it's not counted in the cost of a batch of wine.
But if you're just starting out, and TOTAL price is a big concern, sure go with Zorks. I'm not even sure if I can buy them easily at the moment. Got some at an LHBS in Buffalo, but haven't seen any since. Not sold at my regular store.
Steve